That is a result of 2 mechanics.
1) Help action restoring your HP. Raw you should only be able to get a party member up by feeding them a potion or using a spell, which are limited resources.
2) Action economy (this one isn't Larians falt). Creatures that are designed to be bosses tend to have legendary actions (ability to act more then ones per round).
More slippery slope problems with their hombrew rules. Items as a bonus action? Well we cant have players reviving others as a bonus action, better remove that function of potions alltogether. So how can we bring up downed players? Oh, well just scrap the incredibly usedful command called 'Help' and make that the new +1 potion. By making items a bonus action, they must nerf potions to prevent them from being a healing word on every player... and then we remove the ability to add advantage to an allies attack because we need the real estate.
