You are vastly oversimplifying the problem here. One of the most obvious being, cameras don't really work without light on the subject being captured, and currently Starlink doesn't have a sun synchronous orbit like most (non-SAR) remote sensing birds do. Starlink would need to be completely reengineered from scratch to add even mediocre remote sensing capabilities without degrading the original mission of the Starlink platform (something akin to space mesh networking).

Put simply, it's MUCH easier and cheaper to build one type of satellite that does one task very well than it is to do two tasks poorly.