On Twitter/Instagram/whatever, you're exposed to the arbitrary censorship choices of the platform AND the risk of being deplatformed for any reason. Once that happens, you don't just lose deliverability, you lose every single relationship you had.
With an email list, at least you retain the list should your deliverability tank. It might take a lot of work to migrate to a new non-deny-listed setup, but at least you have a (hopefully double-)opted-in relationship with each prior reader still.
A lot of fairly low quality (but at least semi-legit) newsletters that I probably didn't explicitly sign up for end up in my Gmail SPAM folder--probably because enough people have flagged them as SPAM. But I actually find it pretty uncommon for a newsletter I directly signed up for to end up there.
You are at the mercy of Gmail/Outlook's spam filtering algorithms