My first thought would be that these are often thought of as "uber-cheap" (the compact mini systems) before someone even lays eyes on it or looks up some specs...not justified, but that's probably why there aren't more of them if I had to guess.
Well, I can give you my perspective on this from my personal experience; I have always owned five-disc carousel changers in my home audio systems because I simply don't like the inconvenience of getting up to change a disc once one's finished, or if I just want to hear a song or two from one album, or when I am playing a CD single of which I have a lot of...also, I do a lot of mixed compilation recordings from CDs and CD singles (mostly) which get burned onto a CD-R on my CD recorder, and with a carousel CD changer, I can program the five discs in the order I want them and that way the recording process is smooth without needing to get up between each disc to change them out if I had a single disc player.
Now, that said, the quality of these units has varied; for the most part, I never had any trouble with any of them back from when I owned my first Kenwood five disc changer up until the Marantz CC4001 I have now in my system -- but the 4001 has developed a strange hiccup in which sometimes it will completely ignore the programming I have made for the disc order and it will totally skip over a tray altogether, which forces me to stop the recording I am making and start over. It's a real pain in the ***, and I have contacted Marantz about this already -- they told me it's completely not normal behavior for this unit and I should contact Crutchfield about it because that's who I bought it from. I didn't even bother because the changer is already comfortably installed in my rack/stand, but you are right and that's the point of my post -- these changers aren't really of the highest of quality, that's for sure. The thing is, regardless of how "audiophile grade" the single disc players are, I just don't want to lose the convenience of the five disc carousel and I won't buy one of those Sony jukebox 400-disc megachangers; to be honest I don't think any "esoteric" or "high end" brands make a carousel-style changer that would be of a superior build and sound quality. If there was, I would look into one.
Interestingly enough, Marantz introduced a replacement for the 4001 with a new aluminum/glossy black front bezel.
Of course, I am talking about full-sized CD changer components, not the ones that come with these mini systems, so if that's what you're talking about here, my apologies.