Not true. Navy Federal, for example, is only available to Defense.
Perhaps you're talking about credit unions like the one in my area: UVA Community Credit Union, which does have a community charter and serves its members in several counties in Central Virginia.
However, not all credit unions are of that flavor, and the membership of many remains confined to specified eligibility groups.
Until then, please don't falsely claim that all credit unions offer geographic eligibility rather than those "previous rules" (which haven't gone away at all). It all depends on the credit union's charter.
Navy Federal has opened their membership quite a bit in the recent past.
When I first joined in 1985 even though they had branches in San Diego you couldn't join them there. You had to join overseas on a deployment. IIRC, it had to do with there being other credit unions that were chartered to serve the military in the area. I joined Navy Fed in Subic.
Eventually they were able to sign up Navy and Marines anywhere in CONUS. Then they started taking active duty from any service. Now they even take immediate family if a member sponsors them. My father has a Navy Federal account through me.