Most internet users were given an email address with their service, for free, with no setup, care, feeding, or even a single iota of further thought required. If sending and receiving email back then required as much screwing around then as setting up Mastodon does today, do you think it would be as ubiquitous?
Setting up email back in the day required far more screwing around than Mastodon does today, and despite that email continued to gain more and more traction until it became mainstream and even the most computer illiterate people were able to use it.
With all due respect: bullshit. Again, email accounts were provided for free with bog standard Internet service at least in the mid-90s which is the time I can speak to. Hell, my original ISP as part of the sign-up paperwork included instructions on how to log in with Outlook Express (alongside the instructions on how to configure Windows 95 dial-up networking).
Nobody had to think about where they were registering or who they could reach. Email accounts were fungible. At no point did picking the wrong ISP as a dial-up customer functionally limit who I could email. Mastodon, and the Fediverse for that matter, is far more complicated.
Email became popular and commonplace for "the public" when Hotmail and Gmail came along. Before that, you had ISPs offering some POP3 services which people used to send and receive a few emails per week. Maybe your workplace provided email services.
But the main thing is; people only used email if someone was willing to manage it for them. And they almost always went with the default choice (ISP or work email), later replaced by the most convenient option (Hotmail and Gmail).
There's still lots of people using their 20 year old ISP email addresses because they can't be bothered or don't know how to switch.
There is no default or obvious mastodon option. That's the problem.
Mastodon is also being managed by people who operate the servers, and there are obvious defaults. When you go to https://joinmastodon.org/ it guides you through picking a server. This isn't rocket science and I have no idea why people keep bringing this up as if it was an actual problem when it's clearly not.
Lets say email didn't exist, and instead it came out today, do you think there's a chance in hell it would succeed? Everything in the early days of the internet was difficult in one way or another. Trying to get grandma's AT string right so the modem wouldn't drop at 24000bps and getting the POP3 server was configured was a nightmare. It mostly got easier for the masses when webmail became a thing. But again, I think it would fall on its face if introduced now.
First, it's important to define the metric for success. I would argue that Mastodon is already successful. It's a network that has over a million users on it, and that's growing steadily.
At this point, Mastodon will be around indefinitely, and it will probably outlive every commercial network that exists today. The only thing it needs to stay alive is to have enough users who generate content and run servers, as well as people who are willing to work on the code.
This is the core difference between open source projects and commercial companies. A company has to be able to produce profit, and a large publicly traded company has keep investors happy. Mastodon doesn't need to do any of these things.