A VCR is rather useless without a TV, so it's a natural idea to combine the two together. As we've seen, the first Betamax machine available in the US was a combined TV/VCR, but despite this, and the inherant simplicty of a combined unit, they've never really been popular for home use.

Interestingly they seem to be more popular today, particularly the combined DVD and TV (and the "crossover" DVD + VCR + TV). Perhaps this reflects mainly the extremely low price of DVD players and VCRs -- both are selling for less than £40 at the time of writing, which would make the extra cost on top of the TV itself minimal. Back in the day, the huge cost of a VCR made full-size combis extremely expensive, and of course if one part went wrong the whole unit would need reparing.

A built in TV (or monitor) is much more useful in a portable machine. You could check your footage more easily than squinting into the viewfinder, and of course colour viewfinders were unheard of until the 1990s, so a colour combi would be a significantly more useful system.

Another common use for combination units (or at least, a common marketing approach) was as portable "presentation" systems for travelling salesmen or businessmen. Where today they'd plug their laptop into the projector, in the 1980s they would plonk their presentation unit on the boardroom table and play a promotional video.