I'm not really sure if keeping a strict schedule has any real relevance here, outside maybe PR and politics. Starships will drop the cost to other bodies in the same way Falcon dropped the cost to orbit. Why would anyone want to invest in a technology and a project that will be obsolete by the time it's implemented?
Assuming SpaceX can deliver it. They've failed to do a successful test flight with even a fraction of the officially planned capacity. Who knows how long it will take them, if they can even pull it off, to deliver it.