[scrlk]

The reason why they went down the slot route was for packaging reasons.

Cache was still external at that point. There would be performance benefits from brining it on die, but larger chips are more expensive to make & using two smaller dies (one for CPU & one for cache like the Pentium Pro) is still quite expensive.

The middle ground was to put the CPU and cache on a single PCB, so you end up with a cartridge form factor. By the time the next generation rolled around it was possible to put the CPU and cache on the same die at a reasonable cost (Moore's law), making the cartridge form factor obsolete.