…and this is how you keep people using mainstream services instead of FOSS / privacy respecting ones.

The actual answer is convenience and not wanting to make their life more difficult, which brings ignorance into it.

Not everyone is ready to flip their whole digital life upside down based on the privacy principles you and I care about - that’s why I too use the approach the parent commenter mentioned, and I’m also okay with people who just won’t make any switches, because while I don’t support it, I understand it.