Why don't CPU companies like Intel print Ram next to the CPU on the same chip?

It seems a bit odd to me that in a PC you have a CPU and then you need RAM and then you need to connect them together as separate modules etc.

Why do companies not just print the Ram right next to the CPU on the same chip? Wouldn't that make it much faster and cheaper and also allow Intel to capture a lot of the Ram market? This feels like an obvious move?

I get that you lose the ability to custom choose the CPU and Ram that you want separately but that feels like quite a small deal? Doesn't feel like you really want 4x more or less than the optimal for amount of Ram.