Sometimes the path you take your users through is more important.
Cloud9 was trying to take already established developers and put them into a cloud ide. Repl.it is taking new developers without entrenched habits and hoping they’ll never leave for the traditional local dev environment.
It makes a lot of sense when you view it that way
1, companies all expect you to work in the traditional way with local repos etc. All their tooling is geared towards that. If experienced users who set the standards aren't being migrated over, then they'll reinforce that status quo, and so will people who learned on repl but were forced to migrate off (monkey ladder experiment style).
2., using older tools is a point of pride. There's definitely a strain of "if you use repl.it / etc. and not emacs / vim / vscode you're a noob." This obviously is toxic and not great, but it does exist, and acts as another obstacle to online IDE adoption I think.