But why are SQ-A and SQ-Ai bodies and lenses now so incredibly cheap in comparison to Hasselblad? Are they fundamentally prone to breakdown? Something else wrong? Thanks for advice.
For a number of reasons, Hasselblads are the sexier or more desirable purchase, hence the higher cost.
I've owned and used both systems, and in photographic terms, the Bronica SQ-A is difficult to beat—great cost to performance ratio, less quirky than the Hasselblad with better ergonomics, and photographs look great. Some might state that the Hasselblad is easier to repair, but I've had my Bronica bodies and lenses all successfully serviced and repaired without any problems. Even if you did break a Bronica, you can buy three Bronicas for the price of one Hasselblad, and your Bronica will probably be twenty years younger. That said, I had very few problems and I went hiking all over the place with my SQ-A and SQ-B (I sold my SQ-Ai pretty quickly).
If you're just going to stare at your camera, then the Hasselblad looks nicer. Well, to be fair, I prefer the backs of the Hasselblad system, the easier long exposures, the 110mm f/2 lens (although that requires using the focal plane bodies), and the prospect of using the Flexbody (unfortunately, I sold the system before I got to own one of these).
Certainly, the Bronica system is nowhere near as extensive.
Unless you need one of the specialised accessories of the Hasselblad though, my vote is always for the Bronica (SQ-A or SQ-B preferred to the other models).