Best resources for framework mapping?

Trying to see how different frameworks map to each other or differ; specifically 800-171 and ISO 27001/2. I am finding more organizations ask for ISO compliance over CMMC and I am wondering why this is. My current thinking is international standard vs. US, but wanted to know if there is more to it.

800-171 cmmc compliance current cybersecurity framework frameworks international iso iso 27001 map mapping organizations resources standard thinking