The other thing is that there's no meaningful leaderboard or PVP situations. Some gamers will whale to acquire or preserve a position as #1-on-the-charts, so hyperoptimizing for single player doesn't scratch that itch, unless you're doing some Rube Goldberg setup like self-promoting video streams demonstrating your overpowered build.
I've tossed a little money (probably about USD40 over three years) on Genshin, but I'd rather express my attachment to characters by buying an Arataki Itto oppai mousepad off of Aliexpress. TBH, I found my interest waning when I realized I had a sufficiently capable team of characters I liked, so there wasn't really any reason to go chasing characters I didn't want.