Adding more execution units doesn’t speed up tasks as much as you’d think, because not everything can be done in parallel.

It’s kinda the same way that, for example, one woman can have a baby in nine months but nine women can’t have a baby in one month.

For more info, see: https://en.wikipedia.org/wiki/Amdahl’s_law

Also, even when you can in theory parallelize something, it’s not always easy to figure out how to do it.

The other reason we don’t make chips with thousands of tiny 8086s is that, if we’re making new chips anyway, why not incorporate the ideas we’ve learned in the last 40 years instead of just copying old tech? Not using new designs is kinda a waste.

And if you do incorporate new ideas to make a chip with thousands of execution units on it, guess what: that does exist and is called a GPU.