CPU cache is already used extremely often, far more than any ssd is. It’s purpose is to store data that the CPU (and it’s multiple threads) is working on and may need for it’s next instructions. As you can imagine, with everything the CPU is constantly doing, there’s a lot of instructions and a lot of cache that’s constantly being swapped out for new data.

If anything, using cpu cache as a RAM disk would probably reduce the amount of read/writes done on the cache, as you’re taking away space for actual caching