I'm against paid loot boxes because they prey on people with addictive personalities. There have been stories of gambling addicts who have been advised to play video games instead of going to casinos, only to get sucked in by loot boxes.
Moreover, massive publishers like EA, Ubisoft and Activision don't even need microtransactions to stay afloat. They have a lot of the biggest franchises around and have hugely wealthy owners. Bobby Kotick, CEO of Activision, is a billionaire, and the company has avoided paying billions of dollars in taxes. The wealth could easily be spread around the company without packing popular games with inside purchases, but we're talking about a set of higher-ups who care about nothing but making as much money as possible.
The ability to unlock items instantly or speed up progress used to be freely accessible in games through cheat codes. Frankly, when we're talking about massive corporations like these, I can't see any reason why that isn't still the case other than greed. The Assassin's Creed brand wouldn't go under if it didn't have in-game purchases, and neither would Call of Duty, Grand Theft Auto, FIFA and all the rest. I could maybe understand if a small independent studio did it, but the fact is that they're the ones who aren't doing it, and they're still turning profits if they sell reasonably well.