Remakes of great PS2 games are common these days, and developers say it isn't overly complicated or draining to undertake such projects.
But the reason we're not seeing remakes of classic PS1 games is simple: it's just too hard. That may have sounded like a cop-out coming from Square Enix in regards to a Final Fantasy VII remake, but the truth of the matter is becoming clear. The gap in technology is just too great. We're not talking about a "remake" at this point; we're talking about rebuilding the game from the ground up.
For example, take the recent Metal Gear Solid HD Collection . When announcing it, Konami specifically said they couldn't include the original MGS because it would've taken far too much time and effort. The generational tech difference is just too great, and they would've had to change just about everything; it's no longer an "upgrade" when we're talking about such a project. As another example, remember that Square Enix is doing a high-definition overhaul of Final Fantasy X .
Now, as awesome as that is, you gotta figure that even Square Enix knew the fans wanted FFVII more. It has been talked about for years. But the technical hurdles were just too much for them, and that's perfectly understandable. I do believe that they could easily have assigned a team to the task, taken care of it, and satisfied about a bazillion hardcore Final Fantasy fans, but that's the beside the point. The bottom line is that we're not seeing PS1 remakes for a very good reason.
So you're just going to have to be happy with the PS2 remakes. No, Capcom isn't going to remake the original Dino Crisis in HD. No, Konami won't revamp Castlevania: Symphony of the Night and give us a glorious HD side-scrolling quest. …okay, maybe the latter is more possible, as it doesn't involve 3D modeling and rendering and what-have-you. But in general, just get the idea of PS1 remakes out of your head. Sorry.