It’s been true for a long time. Even long before the lootbox era.

Look at WoW. It was one of the biggest games in the world for the longest time. Randomized loot drops after a boss is very like a slot-machine and addictive, and you had to pay monthly to keep playing.

They’ve discovered that making people pay for each pull of the slot machine is more profitable. But the tactics and design have been around for a while.