The reason for that, is to avoid having influence from outside. Even "angel" investment can be problematic, as the "angel" has the ear of the leadership.
I have found that even well-meaning outsiders can have highly destructive influence, because they don't understand the culture and they aren't the ones on the hook, if things go pear-shaped, as opposed to the ones that have a real, personal, stake (like all those Ello users, who lost so much).
I'm just thankful that mobile phone networks haven't switched to a "free with ads interspersed into your texts" model yet.
(Of course there are still ads in my texts, but at least those are officially spam rather than network endorsed.)
Everyone says they are on board with supporting the little guys, until they hit bugs and start complaining.
Market timing is hard.
It was an X.400-based nightmare, and never took off.
I know some very privacy-focused person (a friend of mine) who will stop being willing to be in contact with you (or being your friend) if you use an email address at one of these big spying email providers to write him an email.
So, it is just a matter of being consequential.
I guess it depends on whether you're looking to achieve something unique and truly new, or just "get rich fast".
Literally in a span of months SMS usage went the way of the dinosaur.