I thought the main reason was because you could only record two hours on a Betamax tape, whereas you could record six on VHS. If you were going out for an evening, you couldn't tape a night's worth of primetime on one cassette with Betamax.
Well, that's also the porno connection. . .
It IS, after all, all about how long it is. . . .
(diving for cover, grinning like hell)
Beta sacrificed time for quality. By the time they offered a "low quality" mode that actually gave you the same quality as VHS and MORE time on a smaller tape, it was too late, and more expensive.
I used to sell both formats back in the late 70's. People wanted the same format as their friends, end of story. It is why people used to compare Apple computers to Beta. But since you can run windows on a Mac now, and you get more for the higher price, it looks like the Apple machines have successfully carved out, at the very least, a "permanent" niche.