I think the biggest issue people point to is you have to sink literally 10 years or $100,000 into the game to fully upgrade a character with how the rewards are structured/priced.
I've been playing Diablo 1 for about two decades, not every day and not every year, but I assure you it is countless hours. I have not found all the items that would perfect my characters. It takes an extraordinary amount of time to find them. Some items I may never find in all my life. I enjoy playing the game. Some people are willing to play, some pay.
So by 10 years I don't mean playing casually for a decade, it's literally 90,000 hours. And Diablo Immortal is a little different being a PVP game, having good gear doesn't just let you solo dungeons, it means people paying their way into kicking your ass every time.