This site has weapons such as the vorpal sword, which is listed as any sword that deals slashing damage, but this option is not available in the homebrew magic item creator, nor are similar variants. Alternatively, there isn't even an option to write your own weapon to suit the nature/needs of the weapon. Is there a reason for this, or did the creators of the system neglect to think of putting it in?

Weapon 'families' exist solely for listings as representative of what exists in the compendium, for example Vorpal Sword. There's no 'Vorpal Sword' in the equipment menus on your character sheet, nor can you copy a generic Vorpal Sword in the homebrew tools, it just gives you the three options.

Because homebrew isn't tied to compendium, it doesn't need that parent item, you cut straight to the various types. You don't need Vorpal Sword because you can go straight to Vorpal Greatsword.

This makes sense to a point, but it's still annoying for when I'm trying to create an item that could be "any firearm" or "any sword". Instead, I have to make each one individually, which is doable, but tedious and annoying.

I believe they make them individually already for the official items, they just also make the parent item to match what's published