You think because theyve spent all this money and resources on infrastructure…

Access to infrastructure you don't pay for or maintain is pure profit

That they want more infrastructure to the point they’d hijack people’s phones and computers to processore data?

Sure there are a lot of data centres, but they want/need more and our devices cost them nothing to compute on

How does that solve the problem of them having too much infrastructure and nothing to calculate?

There are data centres to be with nothing inside, unable to process anything. Can't remember exactly but I did read of a few centres in the US that can't start up