Because with DLC, whatever random stuff that happens, that kind of randomness is part of the game's experience, the buyer gets the product he wants as a one time purchase of something he's sure to get.
Lootboxes include paying money for no return guaranteed, and the most important part is that there is no limit to lootboxes, when game experiences are built around the consuming of lootboxes to get enjoyment out of an already prepaid product, and such propositions are permanent, and the potential spending path has no real limits while still maintaining its random nature, it puts the whole bussiness in charge of the publishers, with zero guarantee to a buyer who might as well spend more money that he has.
And the worst part is that children games use this system. Old ass adults can destroy their finances for all we care, but no government wants to have a big part of its children pool in risk of becoming addicts.
The driving point, is how do you turn that into concise, specific language that can be enforced?
Repeatability seems one of the keys. Real money obviously. As above, there needs to be a qualifier that distinguishes lootbox experiences from things like arcade games. It's a good conversation to be having, as it lets us drill to what the requests we have actually are, clearly.