To pile on, gmail is also well-known to have fantastic spam and phishing prevention abilities compared to most other email solutions, something you could literally never do at home yourself without some incredible software that you run yourself (and even then probably not). That's a huge value-add for a ton of users I'd imagine.

'Nothing to gain' is incredibly hyperbolic I think or this person has never read about gmail/used gmail before.

You seem to care more about the one time setup effort than continuously feeding yourself to Google.

Besides, there are providers like Proton if you can't afford to set one up.