Now if you tried this with a hot bolt and equally hot nut, the bolt would contract along its length, but the threads would get looser so it’d probably still be

Now if you tried this with a hot bolt and equally hot nut, the bolt would contract along its length, but the threads would get looser so it’d probably still be a net loss for clamping load. Rivets, on the other hand, are commonly heated and forged so that both ends have a head, and then as they cool the clamping load increases. This was very common a hundred years ago, but my understanding is that bolted joints provide a more predictable clamping load and that is why they are so dominant today.