I agree generally, but most people I know barely ever check their personal emails, pretty much just enough to sign up for twitter/instagram/snapchat/whatever's popular now.

In what kind of bubble do you live? Most people I know check their personal e-mails quite regularly.

Mostly people aged 18-25.

Ok, then it makes sense. That age group is still considered very young adults, and most are still studying and not even exposed to full time jobs yet. As soon as you receive important emails from banks etc you start checking your personal e-mail regularly.

That works for very niche streamers/creators. Maybe with an older audience as well. If your a streamer on twitch or YouTube chances are your audience isn‘t older than 30. I personally don‘t really use email for actual communication. Twitter is pretty much perfect to communicate to an audience. Yes it isn‘t federated but at least you‘re using a bunch of different platforms to diversify risk.

Generally I would advise new content creators to be present on every possible platform.

I don't use Twitter but I tried it a few years back. It's hard to follow relevant content if half of what you see are people's re-tweets. With e-mail I can easily sift through and find what is relevant to me.