The bug

Probably intentional, see MC-139433. Piglins that are given bows don't attack players, hoglins or wither skeletons. I would expect them to attack like how they use their swords.

How to reproduce

1. Set gamemode to survival
2. Type in the following command given:

    /summon piglin ~ ~ ~ {HandItems:[{id:bow,Count:1b}]} 

   → "Piglin snorts angrily" appears, but somehow is not attacking.

Notes:

• Unlike pillagers/illusioners, piglins can use melee even if the they have item that isn't a melee weapon or unarmed.