Privacy, it is almost impossible in the modern era. But still a bit more under control

Security, it is an illusion, very hard to keep on security

Cost, the hardware, time invested and energy may be higher than standard services

Education, good reason

Because it is cool, yeah it is

Better services, disagree, they are not better, usually clumsy and high maintenance, may work as intended or lack features

There is a simpler reason I like self hosting, I don't want to be subject to the mercy of the changing of rules of a tool I can't manage. Possible closure, increasing cost, features by tiers, I really hate subscription models.