Because most oss maintainers are more afraid of their work disappearing due to service shutdowns than they are being profiled by data miners.
Everyone has seen some example of a tool or resource hosted on a persons private server end up taken down because they couldn’t afford it, the isp or university stopped offering hosting or because they simply couldn’t keep doing it due to death or old age.
That’s what people who create software are afraid of. The loss of that creation, not the loss of the privacy of people who contribute to it or download it.