Because, it is not impossible anymore, it just takes a tiny bit of foresight and preparation.
I'm not going to go into everyone else's improvised shenanigans to bend the rules without breaking them.
Using the scroll was never the issue, granting additional object interactions outside your turn is. If it is ok to draw a scroll as a reaction, why not a weapon? Or why not be able to put away a weapon or wand to cast a spell with an empty hand? These are all things that the rules disallow. That is the issue.
I'm assuming you are talking a wand and shield combo and sword and shield otherwise the other hand is already free.
Here is a tweet from Mike Mearls that solves it. Again he let the player play
Because, it is not impossible anymore, it just takes a tiny bit of foresight and preparation.
I'm not going to go into everyone else's improvised shenanigans to bend the rules without breaking them.
Using the scroll was never the issue, granting additional object interactions outside your turn is. If it is ok to draw a scroll as a reaction, why not a weapon? Or why not be able to put away a weapon or wand to cast a spell with an empty hand? These are all things that the rules disallow. That is the issue.
I'm assuming you are talking a wand and shield combo and sword and shield otherwise the other hand is already free.
Here is a tweet from Mike Mearls that solves it. Again he let the player play
And just because a dev allows it at their table does not make it the rule.
Also, this house rule only circumvents the object interaction rules, it doesn't break them. If MM had said "you can stow and draw your weapon all in the same turn if it is to cast a spell," that would have been breaking the rule. How he answered removes having to interact with storage at all. So you could run this house rule and still enforce drawing a scroll only on your turn without contradiction. It's apples and oranges.
If it's a reaction spell that you're using a lot, like Shield, it's better to just keep it known or prepared. My bard made the Feather Fall scroll for just in case, so that she wouldn't need to keep it in her regular repertoire (known spells), and it only cost 25gp to make it herself so it seemed worth it. This was before Tasha's came out with the Spellwrought Tattoos, and I completely agree that's the better option for a "don't usually need it but when you do, you really need it" reaction spell.
Heck, this would be a way to give one Absorb Elements casting to my Wild Magic Sorcerer's party members who can't get it via their class or aren't Tiefling - the Fireball surge effect was in her backstory so she keeps 20ft away from everyone as much as possible, but it hasn't happened at the table (yet). Maybe her Artificer friend could look into magical tattoos when they get to the city soon...
Coming back to this, I would argue that it is not possible to draw a scroll out of a tube and read it during a reaction- since it isn't possible to draw a weapon as part of a reaction to do an opportunity attack.
I would however, as a DM, allow it if the spellcaster has the Warcaster feat. that feat is specifically centered around casting on a battlefield. /Since that feat specifically allows the casting of spells with 1 action as part of a reaction to make an Attack of Opportunity, it allows for the retrieving of spell components as part of the casting. It would be logical to allow it under those circumstances.
I can see a war mage keeping a yellow card on its belt, pulling it out and yelling "Foul" to cast Counterspell.
I'm assuming you are talking a wand and shield combo and sword and shield otherwise the other hand is already free.
Here is a tweet from Mike Mearls that solves it. Again he let the player play
https://twitter.com/mikemearls/status/504001681689169920?s=20&t=v5dpNp_PKQUjmmosuDGYsg
Or sword and wand, but yeah.
And just because a dev allows it at their table does not make it the rule.
Also, this house rule only circumvents the object interaction rules, it doesn't break them. If MM had said "you can stow and draw your weapon all in the same turn if it is to cast a spell," that would have been breaking the rule. How he answered removes having to interact with storage at all. So you could run this house rule and still enforce drawing a scroll only on your turn without contradiction. It's apples and oranges.
If it's a reaction spell that you're using a lot, like Shield, it's better to just keep it known or prepared. My bard made the Feather Fall scroll for just in case, so that she wouldn't need to keep it in her regular repertoire (known spells), and it only cost 25gp to make it herself so it seemed worth it. This was before Tasha's came out with the Spellwrought Tattoos, and I completely agree that's the better option for a "don't usually need it but when you do, you really need it" reaction spell.
Heck, this would be a way to give one Absorb Elements casting to my Wild Magic Sorcerer's party members who can't get it via their class or aren't Tiefling - the Fireball surge effect was in her backstory so she keeps 20ft away from everyone as much as possible, but it hasn't happened at the table (yet). Maybe her Artificer friend could look into magical tattoos when they get to the city soon...
why not just have the scroll attached to a shield, or to own's forearm, just to have it ready to read at all times?
Coming back to this, I would argue that it is not possible to draw a scroll out of a tube and read it during a reaction- since it isn't possible to draw a weapon as part of a reaction to do an opportunity attack.
I would however, as a DM, allow it if the spellcaster has the Warcaster feat. that feat is specifically centered around casting on a battlefield. /Since that feat specifically allows the casting of spells with 1 action as part of a reaction to make an Attack of Opportunity, it allows for the retrieving of spell components as part of the casting. It would be logical to allow it under those circumstances.
I can see a war mage keeping a yellow card on its belt, pulling it out and yelling "Foul" to cast Counterspell.
If the caster with the counterspell happened to have it out conveniently ready to read, then sure but that would be exceedingly impractical
Depends on how long the scroll is and whether it is in position to read while actively using the shield