what's the difference ...
ISO standards are literally international, where as NIST is US-specific.
ISO standards are available FOR PURCHASE and are copyrighted. NIST as a government organ of US, cannot publish anything other than public domain.
ISO process is influenced by any and all parties of interest, and have to compromise under them. NIST is influenced by US eco-political players and policy makers, and in the infamous Dual-EC-DRBG case, NSA.
I'm a lurker on the POSIX and IEEE754 mailing list, and occasionally see non-technical business discussions. Both POSIX and IEEE754 are republished as ISO/IEC standards outside IEEE.
If you're looking at the stats in US and on the Internet, then NIST standards have higher adoption. If you look at global-regional stats, it varies from country to country.
For trade/econony treaties such as RCEP and Eurozone, some digital signature standard have to be established for authentication of electronic records. This is a major usecase for non-NIST algorithms