I don't know if I fully agree with this -- how many people were actually self-hosting cal infra? I def could be wrong though
The issue isn’t would-be customers going to the trouble of self hosting to save a measly $30/month.
The issue is competitors popping up to clone your offering with your own codebase.
it's not necessarily about people self hosting it, it's about people preferring to pay for hosted stuff that is open source (e.g. I pay for Plausible).
Now it's a lot easier to rewrite open source stuff to get around licensing requirements and have an LLM watch the repo and copy all improvements and fixes, so the bar for a competitor to come along and get 10 years of work for free it a lot lower.