The main problem with lootboxes in video games is that they are designed to manipulate you and trying to divorce the "spending money" part from the feeling of reward. You don't spend money directly on loot boxes, you spend it on a bullshit currency, which you can then use to buy loot boxes. So you don't feel like you are spending money when buying lootboxes, and these lootboxes then use all the psychological tricks that gambling uses, too.
I actually think that TCGs and collecting card games are problematic in a similar way. They are gambling which preys on children. And they should probably be looked into, too. But they at least leave the money connected to the thing, so the children notice that they are spending money, and how much they are spending on it. I would bet that most people who buy lootboxes greatly underestimate the amount of money they spend on them, because they are removed from "real" money by so many steps. Money on a credit card doesn't feel as much like money as cash. Using internet money on your phone feels even less like real money. And the bullshit ingame currency is even further removed from the actual money.
But as a gamer, my main reason to dislike lootboxes is pretty simple. They make games less fun. Games with lootboxes in them are no longer designed to be fun to be played, they are designed to make you desire spending money on lootboxes. This means stuff like earning cool cosmetics in game are basically gone. Which was something i found fun, and which doesn't exist anymore, because companies realized that they could just demand money for the things.