I will admit that some people really do want cosmetics and will go out of their way to get them. I have a friend who really likes collecting "everything". The end result is us playing mystery heroes with remarks from her like "I hate mystery heroes so much" because it means 3 extra loot boxes a week. (I like mystery heroes, though. That's why I play it.) But maybe that's the beginning of a problem.
Furthermore, the scale and ease of purchase of lootboxes vs. baseball cards are incomparable.
It's probably worth differentiating tradeable loot boxes, which end up used like stock speculation, from untradeable ones, which seem to be used more like slot machines.
I purchased a completely random lot of Magic the Gathering cards from someone getting out of the game. I turned around and parceled the cards out for a profit.
Those cards had monetary value at least twice beyond the initial purchase - to the purchaser as he sold them to me, and to me as I sold them to someone else. And that's beyond the value of playing the game.
Good Magic decks range from "not cheap" to "breathtakingly expensive", but no one assembles tournament-level decks purely from opening packs; they buy at least some of the cards from aftermarket sellers. That's a fixed price for a known good, which gives some confidence that people are making rational buying decisions even when they spend a huge amount.
Even casual players are quite likely to open packs, find some things they want to build around, and then fill out what they need by trading or buying. It offers a backstop on the entire system that digital and especially non-transferable products simply don't have.