Because I still don't see the value add.

Everything they offer is already something that SublimeText+Plugins offers. Except I have more control over SublimeText and its Plugins and the configuration of those plugins.

I'd actually love for someone to explain why they use an online code editor, for those that do. The only feature I could feasibly see is collab coding and that sounds like a nightmare and not a benefit.

Because I don't always have internet access. Besides my MacBook Pro is perfectly good as a code editor and in many cases quicker than when you have to put up with network latency.

they depend on the browser which can do things like suspending tabs or crashing