A bit of a heavyhanded way to put it, but one of the strengths of Ableton in my experience has been how easily you could import third-party plugins to supplement the lackluster native tooling. If you can't bounce those plugins to the Push along with a project, that severely gimps the functionality.
it's a sequencer!
Well, no. It's a groove-box, it can produce sounds on it's own. Think Ableton Light (real Lite, not actual Lite) in a box.