Sure, there were people who ran BeOS full-time. But 'preferable to an enthusiast to Linux in 1997' is too low a bar for 'basis for a consumer OS'.
In any case, NextStep didn't do anything in the short run for Apple -- it took dozens of engineers about four years to turn NextStep into OS X, and it's hard to believe that they couldn't have done the same thing with BeOS.
I think it's very easy to believe if you compare them technically. I'm happy to get into that discussion if you're interested but it seems obvious to me a complete, mature OS that was (at the time) considered fairly advanced technologically, had a track record of being ported to every architecture available (along with a track record of running inside/alongside other environments), plus the team that built and maintained all of that was a saner choice than an unfinished OS. Finishing an OS was precisely the problem Apple had for years and was trying to buy its way out of. BeOS and NextStep were not anything close to the same starting point.
I think the biggest difference was vision: BeOS was shooting for the creative media market, while NeXT's biggest successes had come in very enterprise-ish verticals.
I think there's some truth to this, in that Apple's computers had long been pariahs in business settings and getting out of that rut was a thing Apple wanted to do. I imagine it was a factor. At the same time - there was probably way more actual prosumer and creative professional software for NextStep than there ever was for BeOS and much more importantly - Apple was looking to buy technology, not vision.