How do you get data to all those cores? Think about it like this: imagine a restaurant with thousands of one person tables packed as tightly as possible. How do you get customers to/from the tables and how do you get them their food and clear their empty plates?

When it comes to modern processor designs, a large amount of the area on the chip is simply dedicated to solving this problem: getting data into the chip, caching it, and getting the data back out to the rest of the computer.

If your chip is just a massive grid of identical cores then you’re going to have extreme issues keeping them all fed with data to work on. What you likely end up doing is having a bunch of the cores spending a lot of time doing nothing other than acting as intermediaries that pass data along to inner cores for processing.

If you’re doing that then the advantage of having all these identical cores goes away and you’re probably better off replacing some of them with specialized hardware for solving that (IO ports and large, fast caches). But then if you continue that line of reasoning you get to the current designs which are already out there!