Why ? Because ISI separate them ? If you look at the Kodi / ZR it comes out on top of other ISI cars as well, why ? I would suggest something in the naming, packaging or rules makes it that way. Then again not all ISI cars are in order either, maybe different package ages contributes. I can only give you work around, make specific mods that do not have huge or muddled filter lists. Why anyone would want to use all cars-tracks is beyond me, it is there for the uninitiated newbies and it is slower and clunkier loading then mods as well.
Agree 100% The whole AI opponent selection system in rF2 is totally user UNfriendly as is the setting up the VMod for servers. There has to be a total revamp to make it simple to use and build 'car sets' especially to attract new drivers to this great sim.
Setting up vmods is fairly easy without multicmps. Select cars, tracks, fill in some mod info and package. It's not hard just a little bit time consuming if you want to have some spontaneous events with your friends. IMO they should develop the alternate server further (which I hope has already happened because of steam release)