BUG SUMMARY:
Skeletons are supposed to pick up/prefer other bows if the bow is more powerful than the one they are currently holding, however they ignore any bow they are given that is superior.
HOW TO RECREATE THIS ISSUE:
Enable the Mob Griefing gamerule.
Turn the difficulty to Hard (To increase the likelihood of a Skeleton picking up the bow).
Enchant a Bow with any enchantment, such as Power V, etc.
Spawn a bunch of Skeletons.
Throw the bow into the crowd of Skeletons.
Observe that none of the Skeletons pick up the Bow.
Try throwing in a Sword to see that they will are capable of picking up a Sword, but will just not pick up a Bow.
REASON TO FIX THIS BUG ASAP:
This is a niche issue, however any players who would like to use this feature in custom map creations, such as mini-games or adventure maps, cannot have powerful/deadly Skeletons, limiting player creativity.
Still present in recent updates.