Funny to think that instead of curing diseases or making cheap renewable energy, we'd instead try to spend resources to invent a computer to do that for us...
We do that for ourselves when we learn first about something, plan ahead, and then do it. Thing is, we don't know how to cure diseases, we don't know how to make cheap renewable energy, and we certainly don't know how to turn Earth into Heaven. The direct approach might very well be harder than the AI one.
To put it lightly, it would automate and massively bring down the cost/increase the speed of research and engineering. Sure enough money, spent on enough humans, given enough time, could eventually find a cure for any disease. But why do that when you can just ask the AI and have a cure overnight?
Of course it's not clear how safe such an AI would be (such a being could easily outsmart us and get what it wants, whatever that even is), nor how difficult it will be to create one.
The effect of scaling things up should be interesting though. Perhaps there is a "Phase transition" like thing, where suddenly something awesome happens. This also means that, sadly, Universities would no longer be able to provide adequate resources for research.
However, if you see it as a pragmatic problem, then maybe the answer to why not? is because we need better ways to process information -- and this kind of unsupervised machine learning is critical to doing that.