Yeah, it's a chicken and egg problem. Old software doesn't use many cores, and even new, single threaded one doesn't (Javascript, Python, Ruby, etc.).

Because software doesn't really need many cores, no need to create CPUs with many, many cores.

I imagine the cycle's going to break at some point, after all we can only ignore having many cores for so long. Especially that now even mobile devices routinely have at least 4 cores.