"For me, it's not the gambling aspects of it, per se. I am an avid Magic: the Gathering player and never decried the way its loot boxes (boosters) work. It's the fact that, the way these boxes have been handled by many games noticeably warps the design goals of the game from "make an engaging experience" to "motivate the player to buy more loot boxes".

What I mean is that many modern games have loot boxes or microtransactions permeating its design to such a degree that most features seem planned around how they motivate players to spend more money in-game."

Star Wars Battlefront 2 at release was a perfect example of this. The entire experience was built for someone to either grind incessantly and/or spend real money to acquire currency to unlock items as only weapon mods were acquired via accumulated experience and not loot crates. Even the awarding of credits were loosely tied to performance. The "level" of a hero/trooper/ship was the number and rarity of star cards you had, not how much you had used them. There was no shared marketplace so the only way to get a certain emote, or pose, or star card was getting lucky and pulling one. It was often the case that you would pull items for troopers/heroes/ships that you would barely (or never) use.

As a result of all of this you ended up with things like "rubber banding" where players would use a rubber band on their joystick to prevent themselves from being booted from game modes. This had a particularly harmful effect on the Heroes vs. Villains game mode, as its small number of participants (4v4) and scoring via target system meant having one or more "rubber banders" on your team put you at a severe disadvantage and wrecked the experience.