20 years ago, and of course before then in the dialup age, your ISP operated your mail, so there was plenty of competition. Free at the point of use mail which meant you weren’t locked to a single ISP so there were benefits, but the big benefit was the unlimited space that the funding of companies like google allowed for, they could muscle in and knock out competition.

Eventually isps stopped providing as demand was tiny and the cost outweighed it. Same with things like nntp servers.

I pay a couple of quid a month to Zoho to provide my mail, off my own domain. Obviously I have static ip4 and 6 addresses from my ISP, but I’m happy to outsource as long as the cost is transparent and I’m not locked in, so I do. Part of that is to fund companies which are better armed to fight against monopolistic email practices than I am on my own.

There are other suppliers I can shift to by moving my MX records and updating a couple of TXTs, but there’s no need to at the moment.