It wouldn't surprise me at all to find that a high proportion of people prefer physical slide-out keyboards to touchscreens, however, they also prefer nice, slim, lightweight, "sexy" phones, over bulky ones, and adding a physical, slide-out keyboard will make a phone bulky. The two are, quite simply, mutually exclusive.
For the younger generation, the aesthetics and degree of cool associated with a particular phone are massively important, and as a significant phone buying demographic, who've grown up with touchscreens, they are understandably very influential when it comes to designing phones.
Battery longevity is also a major concern for most people, and even if you could come up with a very desirable phone which had a slide-out keyboard design, I'd be surprised if many would go for that over an identical phone which offered a much longer battery life due to being able to fit a larger battery in the same physical case, by removing the keyboard and sliding mechanism.
From a design point of view, modern phones have few if any moving parts, which has a whole host of benefits from increased reliability, to reduced manufacturing costs, and ultimately lower retail price.
A better question for Bennet to have posed would probably have been, "Would you rather have a physical keyboard, or make do with a touchscreen and have a slim, more reliable phone with much better battery life?"