If Gmail proved anything, it was that people would, for the most part, accept any terms of service. Or at least not care enough to read the fine-print closely.
My 20 year old Steam login uses a defunct ISP email from the dial up days. I changed the actual email associated with it for passwords etc. but my login is still “deranger@oldisp.com”
But the point I was trying to make is email has always been free or included, in my experience. The fact Gmail was free was never the draw imo.
I think the major thing Gmail brought to the table was 1GB+ email storage when most free options at the time it was 1-5MB or so. I remember it being an insane increase in the available storage.