Here's the thing. Lootboxes are content, just stripped from the game, and charged at a premium. Shadow of War is a blatantly obvious example of this, where the Orcs can be bought outright. For games like Destiny, the bright engrams are a disassociation of loot from the bosses. I played Runescape, so I'm gonna use it instead of WoW for this comparison: It would be like killing the King Black Dragon and getting a godsword from a lootbox off a drop. It makes no fucking sense. Why even create the boss fight to kill Gough in Dark Souls when you can just sell the armor, either in a lootbox or outright.
These are blatant examples in the past where things could have easily been cut from the game, turned cosmetic, and sold wholesale. I can't give any examples of cosmetics in games recently because I don't play games with them, it just props up the playtime of the game, extending it's perceived life, it's not worth it. A blatant one I can think of though, is Overwatch and their skins. Complete the holiday event? Get a fucking holiday lootbox? Remember in any other MMO with holiday events where you just got the item instead?
I would rather they not faff about designing lootboxes to look enticive and the systems propping them up, and instead see a fucking dungeon with the item at the end. Like it or not, lootbox development time takes away from actual game design time, and by nature cuts content in favor of selling more art.