Probably because a significant proportion of the information seems to suggest the claims rest on "crimes" that wouldn't be prosecutable in the UK and that at least one of the claims seems to have a lot of "retribution of being lied to/cheated on" attached to it.
He didn't jump someone in the middle of the night, it's a far more subtle argument than that, including women finding out he wasn't just sleeping with them..
Then there is the previous dropping of the prosecution and the absolute mess of a procedure that has lead to him being in an embassy for 3 years, willing to be interviewed and not.
None of the above is suggesting he shouldn't be interviewed and tried, however it leaves huge cracks in the case and the seeming proclamation by many on this board that he "obviously" is guilty. So no, it's mostly not apologising for rape, its understanding that the case isn't as clear cut as many make it seem and that the prosecution has made a massive hash up.