While perhaps the video image recorded and played back by Betamax was better, Sony had a smaller tape cassette mechanism that could only record one hour. JVC designed it's cassette to hold two hours of tape. Most consumers were more interested in the extra recording time (which was long enough to record most movies on one tape) rather than a noticable but still marginal superiority in picture quality. The advantages of Sony's U-loading versus VHS's M-loading system were only of interest to videophiles. Sure special effects especially fast forwarding were easier to do with Sony's system, but consumers mainly wanted longer recording times.
I never understood why Sony couldn't just make their tapes, you know, bigger and capture a billion-dollar market.