The in-flight break-up rates of most single engine airplanes with retractable landing gear were significantly higher than for other categories of general aviation aircraft
Sure, but because they are more slippery (and thus a pilot not paying attention will end up exceeding Vne sooner), not because they have retractable gear.
The availability of reasonably slippery fixed gear GA planes capable of ~ 150kt+ is a recent thing. It was done as a marketing stunt in the USA, where the insurance companies are throwing their weight around more than here. In reality it was just a stunt and hasn't worked because the premium on say a Cirrus SR22 is most definitely not lower than on say a TB20/21. But if you have a relatively inexperienced pilot then the "simplicity" of fixed gear is a rewarding yarn for the salesman to spin.
Fixed gear is itself a compromise. To make it low drag you have to have tight wheel cowlings, which compromises grass field / general dirt runway capability. Even the much looser PA28 cowlings are routinely dumped to avoid these problems - look at any flying school fleet.