Cloud sync + 10gb storage space comes with a cost
I can buy a private VPS for $20/yr with 30gb of storage and slap sync thing on it, and find an existing markdown editor if I wanted.
That could easily pay for itself with 4 users. And that's just scraping the bottom of the barrel of low cost servers.
Yes not everyone can set up a server, and yes this takes the burden off spending time doing that. But your average software engineer with some server knowledge could set this up in a day.
The value proposition is just not there.
If I'm building something that needs to "stand the test of time", I find a day lets me relax, meander, think it through, and not get stressed over not moving fast enough.
I've also learned from experience to always over estimate these things ;)