Like half the population of this site exists because Reddit locked down their API. It's an empirical fact that they engage in bot detection and prevention. Anyone who consistently uses a VPN will have personal experience with it. Anyone who's tried to interact with a social media's API can tell you that. Try to write a bot that scrapes Facebook events or LinkedIn profiles before you speak in such absolutes.

You are correct that they don't aim to completely eliminate them. They might even explicitly allow some of them. But If they didn't engage in any bot management you'd see nothing but spam for "hot 21yos in your area" on every site. Depending on the platform they might offer paid API access to facilitate those influence networks (eg X.com blue checks). Even if they did that they'd engage in bot prevention for bots that aren't paying.