There are theories, not generally accepted in mainstream biology/anthropology.

One is that our ancestors lived in coastal areas, where seafood made it much "cheaper" (in the evolutionary sense) to obtain the kind of fatty acids needed for growing a bigger brain.

https://www.psychologytoday.com/blog/lives-the-brain/201001/...

I think the gist of it is our increased brain capacity let us acheive more with the tools, and more importantly to propagate knowledge of developments over generations because we lived in interconnected groups, societies, better communicators perhaps.