Oh you can... you can make it so any item such as a token you purchase for real world money or purchase with a currency that is linked to real world money cannot effect drop chance. Because that can only effect players negatively unless they pay up, its not that you get an improved drop chance if you pay up, it's that regular drop chances are nerfed unless you pay, that's how they design them.
They can still have those items, but they then need to be earned ingame, not by paying.
Alongside a ban on regular lootboxes of course, the fact other countries that already regulate and ban lootboxes immediately recognised diablo immortals dungeons as such and banned it show that it can be done legislatively and has done already.