USB A extension cables exist and work very well, so I'm not saying this is justified, but...
My guess for the rationale behind the explicit ban on female USB A cables in the spec is that signals degrade over distance and they didn't want to try to go to the extra work to make USB host and guest devices hardy enough against noise in the signal to work reliably even in the presence of extension cables.
Apparently USB host/guest devices are hardy enough against noise to handle extension cables just fine. But I'm thinking that wasn't planned to be the case by the authors of the spec. Perhaps most USB host/guest devices exceed the spec in at least that particular regard.
Clearly not all female USB A ports are banned by the spec. Female ports on USB host devices, of course, would have to be allowed or USB would be useless. Given that, I'm guessing an active (powered) extension could be strictly compliant with the spec. (Think of it as a one-port USB hub.)