The reason is old hardware support:

The reason for all that was a compiler flag. When Red Hat builds RHEL, it picks a minimum CPU generation the software will run on. RHEL 9’s cutoff already excludes CERN’s oldest boards, the kind running chips like Intel’s old Core 2 Duo, which comprises about 47 percent of their fleet.

RHEL 10 raises that cutoff again, and this time even newer Ivy Bridge-generation boards, another 17 percent, fall on the wrong side of it.