Not sure if the "leftists" you're referring to is Euroamericans or Chinese but, with all due respect, I'd hate if my preferred national social media was suddenly flooded by confused usians. They tend to make everything about themselves and can't comprehend not being the centre of digital spaces.
China may be socialist, but that doesn't mean that every Chinese space needs to be about socialism, specially not about propagandising foreigners about socialism.
I'm happy using the app, but I'm well aware that I'm a visitor somewhere I don't automatically belong and which is not about me. US people are not used to that dynamic in digital spaces and I don't blame longtime users for being against that.