Eclipse is known for being clunky, but at least it is _known_.

It is also trusted. When I wrote my first Android app, it was the only practical way to write and test. Not sure if that has since changed (am no longer doing apps), but my guess is that a lot of people have Eclipse on their system.

There is a saying that even negative publicity is still publicity.

The most important thing that Theia needs to convince would-be contributors, is that they will still be around tomorrow. Eclipse has been around forever, and most devs assume it will stay around. That has a value that should not be underestimated.