Earlier quoted context omitted.
It was done. There even was those small banners that said something in the way of "if you have gmail I won't mail you" etc. Thing is, the broader public don't care. The difference between gitlab and gmail is primarily that developers care more about this stuff and value their code more than most people care about their email. They are also much more informed in the matter, most using gmail haven't got a clue.
There's a difference between gitlab and gmail. People pay for gitlab while gmail is free. Google can easily declare "either you take it for what it is, or leave." Gitlab can't.
I understand the reticence towards third party telemetry, but refusing basic interaction tracking for a product you pay for is just hurting yourself, even if you're already satisfied with the service. You don't go to the doctor for a checkup and then refuse bloodwork. Obviously there are rules around privacy for medical records that don't exist for interaction tracking. But I don't think the solution should be to get rid of tracking entirely, it should be to extend reasonable privacy rights and protections to our online data.