Absolutely true, and although I did pay for Overleaf at first, I stopped paying when I realized I didn't need the for-pay features anyhow. They made a conscious decision to focus on internal development and I'm OK with that -- Google isn't open-source either (certainly not all of it, and when I was there, very little of it), and I'm OK with that too.

https://www.overleaf.com/help/17-is-overleaf-open-source#.WB...

An open-source business that doesn't survive (cough ReplicaDB cough) isn't necessarily better than a closed-but-extensible one that does. LaTeX itself is, and anything you're working on within Overleaf can be exported as text at any time, so I don't worry so much about lock-in.

The underlying toolchain (LaTeX and packages) is fully OSS, and isn't going anywhere; I have supported the LyX project in the past, and indeed that's how I laid out my dissertation, but in the end I find Overleaf more usable.

I still wish they'd support Markdown, though. Sometimes I just want to run off a quick, properly typeset series of equations and lists/tables without all the boilerplate. I suppose you could make the argument "well, if it was OSS, you could just patch it yourself!", and you wouldn't be wrong. But we use the autosubmit feature a lot, so on balance I've decided I can live with this shortcoming.