50,000 people have already answered, but here's my two cents, too..
Even as someone who perfers a slide out keyboard (Droid 4, here. Probably the last of the good slideout keyboards) it probably comes down to manufacturing costs..
it costs less for softkey phones, less moving parts, infinitely remappable keys, et al..
i rely on my hardware keyboard, cuz SSH. I mean, not losing screen real estate just to get a terminal is worth it..
i realize this is a minority reason for a good hardware keyboard, but yea.. i can type without looking, i can type FASTER..
softkeyboards only exist to make all typists equally crappy typers.. but because the problem is money, you can bet hardware keyboards will never come back.