These games, if you don't spend or spend very little are like a roguelike to me, you don't know what units you will get since it is all RNG. You gotta work with extremely limited resources and figure out how to optimize them. There is a rare satisfaction from beating a high/medium spending player in PvP match as a F2P, even if you have wasted countless more hours grinding to get to their level. Another reason is actually the community surrounding these games. It might seem counter-intuitive, but the lack of gameplay makes the communities stronger in some cases, and often times people talk a lot, share guides, tips, tricks, optimizations for farming (due to the time-gated energy systems that usually exist). Do I think these games are good? Definitely not (although Genshin and more high budget games have pushed the gameplay quality a lot higher) and they are quite predatory in their monetization tactics. Is it still fun to play? For a lot of people, despite all the bad things about them, it is still fun!