Even if you took the hardcore view that loot boxes are outright gambling, gambling isn't illegal for adults. Why would loot boxes be treated more stringently than online casinos, even in your scenario?
Also, it doesn't incentivize age verification systems, age verification systems are now mandatory. They are needed to be able to sell any games marketed at adults, including porn games, games with loot boxes and presumably any other game with an 18 and up rating by their official ratings board.
The loot box panic has mostly been another variant of the "will someone thing of the children" violence panic of the 90s. Just like then, age ratings and parental controls should have been the solution, but because gamers were too busy being angry and self righteous online they went with it to this point.