You can actually repurpose a starship as a space station. ISS is 915 m^2, starship should be around 1100 m^2. Now imagine using several repurposed starship as space station modules..

Rockets and space station have very different material requirements.

It makes way more sense to launch the whole space station in one piece. ISS is how it is because they couldn't.

But why not build an even bigger space station by combining payloads from multiple launches?

Possibly, with bigger modules, you could build it in a way that each module is fully redundant, has its own power, thrusters, docking, etc. That way you'd have a fully operational station from the first module, and great redundancy if there was ever an accident.

We hardly have any use for the one we have. The best that could be done is one cheaper and better suited to the few uses we have discovered.

Instead we are intent on crashing the space station into the ocean.

Without the space shuttle, ISS has lost its reason to exist. Without ISS, the shuttle would have had no reason to exist.

The ISS orbit naturally decays without regular boosts due to atmospheric drag. I'm hopeful that Starship is fully operational by the time the ISS reaches EOL, maybe a few Starship launches would have enough delta-V to push the ISS up into a graveyard orbit.

NASA has a commercial station program ongoing and they are handing out contracts.

BlueOrigin suggested station does have modules far larger then current ISS, but its attended to be launched on New Glenn, not Starship.