I don't want to sound Clintonian, but it depends on what you mean by "ability". The ability that's lacking is the psychological ability. That is, they could, but for the fact that they absolutely do not want to and could never bring themselves to. An anology (except for the fact that this is a sin) would be the fact that just about everyone could commit murder, but most don't have the ability to actually do it. This inability isn't just reprobates, it's everyone. It's external grace, not anything in a person's nature (whether from his own efforts or from something hard-wired to begin with) that causes the change.
Then God does create some beings He plans to simply destroy, no? He creates them without the psychological capacity to resist sin, and does not supply the Grace necessary to save them; thus, He creates them to consign them to eternal torment.