It likely exploded because they blew it up (flight termination system). It looks like the stages failed to separate and it started to spin. In this case they don’t let an uncontrollable rocket just fly off and see where it comes down, they blow it up. The FTS is basically an explosive mounted to the rocket that can be remotely detonated exactly for situations like this.

>> It looks like the stages failed to separate and it started to spin.

Most complicated part of building any rocket by far and Starship's is a lot more complex than any previous one by far. It was always the most failure prone part but everything else looks great.

I kinda wish they'd have let it keep going in order to get the telemetry.

The altitude and velocity when things went sideways were in MRBM territory, not ICBM territory so the only thing they would have hit would have been the Atlantic ocean.

they let it go well past the point it was clear to lay observers that it was out of control. i expect they got all the uncontrolled-descent telemetry they really had a use for.