when attempting to /summon in a pillager it will have the CanPickUpLoot as 1b

same goes for pillager_spawn_eggs that are given to the player via commands with EntityTag data (even if it's empty)

Any attempts to change this via including CanPickUpLoot:0b or CanPickUpLoot:false in the command fail to change the outcome.

and yes, /data modify also fails to alter their state.