It does not matter if you do not use GMail, google/microsoft/<insert any other popular email provider here> has all your emails anyways, since everybody sends you emails from those domains.
Quite the difference between <insertproviderhere> having all your emails and <insertallprovidershere> having all your emails if they were to pitch together.
Huge difference between Google being aware that an email alias <name>@<domain> exists and it having access to the contents of all your emails including purchases, subscriptions, login patterns, GPS data, connections to other emails, etc.
And if they didn't get it from Google, they'd get it from someone else. Just like they did for centuries before email came around.