Armor, shields, martial weapons, spell caster items, all locked away from a monk.    And it's more than 1 dpr past tier 1.   Since monks can only use simple weapons you're looking at choices like using a 1d4 dagger with nick (useless because you lose flurry of blows access if you use the feature for your extra attack) or a 1d6 hand axe with vex vs your 1d10/12 fist. You're also locked out of all feats that require you to be proficient in a martial weapon.  Could you use a feat to get proficiency? Sure but then you fall behind your already problematic AC curve, and you lose your bonus unarmed strike if you are wielding a martial weapon.   

Hi!  Quickly chiming in.  Monks' magic item issues - many of their features key off unarmed attacks, of which there is a singular tattoo to boost it as a "weapon." They can use maces or staves, of which there are a very few, and only work for half the monk's attacks.

Monks may use many robes or bracers of armor. These are mostly aimed at wizards, warlocks or sorcerers.

Monks have no issue with non-armor, non-weapons.

While there are indeed many items they can use, the weapons and armor are few, not obvious, and not necessarily great for the monk.

Any magic weapon can be retooled into any other weapon of a similar type without issue, it's in the DMG; a Flame tongue can be a quarterstaff or mace or sickle. On that topic, weapon options aren't nearly so limited by masteries, although admittedly Flex is pretty useless for a Monk. Nick arguably stacks with Martial Arts/FoB, as the Martial Arts bonus attack option is distinct from the Light property or you can use a Mace for Sap which is a decent recurring debuff option. Pure unarmed does need some support in that area though, unless they feel that's covered by the aforementioned class features. Regarding the issue of armor, magic armor is weighted heavily towards Heavy, which only Fighters and Paladins have access to as a class, so that's less a matter of "Monks are specifically deprived" and more "only Fighters and Paladins get at the good stuff". Some kind of +X item for unarmed strikes would help support pure unarmed builds, but once again they're not nearly as deprived as people make out based on my analysis of the material.

The big problem for magic items and monks is that there aren't any items that boost unarmed attacks that don't cost an attunement slot, whereas generic magic weapons do not require attunement.

Quote from Pantagruel666 >>

The big problem for magic items and monks is that there aren't any items that boost unarmed attacks that don't cost an attunement slot, whereas generic magic weapons do not require attunement.

Same is also true of armour; so if other martials in the party are rocking both, the Monk is effectively two attunement slots down. While a DM is free to customise magic items to suit players, they shouldn't need to; the basic mix should be balanced enough to avoid having to do this (and to cater properly for Adventurer's League).

I always thought D&D was missing something like '+2 Boots of Ass-Kicking'. People seems to focus on Monks punching, completely ignoring the fact a significant number of unarmed combat forms use kicking, kneeing, elbowing, etc. :)

'These boots were made for kicking, and that's just what they'll do.  One these days these are gonna stomp all over you'

Quote from HeroZero >>

'These boots were made for kicking, and that's just what they'll do.  One these days these are gonna stomp all over you'

 Nice!