It still is. But nobody is using that feature. People choose to centralize and visit the same 10 sites and to avoid self-hosting.
Nothing is preventing society from using the internet in that way, but it's sooo much easier for the average non-tech person to not self-host an email server versus using something like gmail. It's the same reason I do not own a lift for my car.. sure technically I can install a lift at my house for my car but then I have to maintain it's hydrolics and I'd only use the lift once or twice a year ... who has time for that? Especially if my thing is fixing piano's and not cars. Let the car people handle cars, let the piano people handle piano's... I think we are in the same situation with tech.
Nothing is preventing society from using the internet in that way, but it's sooo much easier for the average non-tech person to not self-host an email server versus using something like gmail. It's the same reason I do not own a lift for my car.. sure technically I can install a lift at my house for my car but then I have to maintain it's hydrolics and I'd only use the lift once or twice a year ... who has time for that? Especially if my thing is fixing piano's and not cars. Let the car people handle cars, let the piano people handle piano's... I think we are in the same situation with tech.