Why is re-baking very very slow?

I did a rake posts:rebake_uncooked_posts command and boy was that a mistake! :joy:

Firstly, I didn’t expect there to be thousands of uncooked posts on a relatively small test site.

But even then, why does it run so slowly? It’s running at a speed that I might expect a ZX Spectrum would to process such a task.

What’s the performance limiter here?