Because TB combat is slow and retarded. RTwP is superior in every way imaginable.
This is going too far in the other way. You realize you can pause in RTwP, make a cup of coffee, do some exercises, shag your wife, go shopping, and come back to the game, right? That's the thing, with RTwP, provided the game gives you as good information as a turn-based game would (e.g. inspection), then every time you pause it's really not so unlike what you're doing in a turn with turn-based. You can spend as much time as you like measuring before you cut, just like in turn-based.
It's just that it's not forced on you, and you don't have to do it for every single move, wait through animations, etc. IOW, RTwP encompasses the fact that in a lot of fights, even tough ones in turn-based, a fair number of actions don't really
need you to look that closely into them, there are often only a small number of viable options anyway, that you can leave to the AI (especially if the game's given you some control over the AI's brain, which gives you
another interesting layer of gameplay to play with).
On the other hand, if the gameplay is rich with simulation and "neat tricks," and you have more options, you
want to have the turn-based effect, which psychologically clears you mind for each character's move so that you look into each character's move options in the most minute detail. And if the design, encounters and gameplay are set up for that, it's very rewarding too. With turn-based, there's a psychological sense of settling down, cracking your knuckles and rolling up your sleeves for each move, which is very addictive.
I dunno, it really baffles me how people can
really hate one or the other mode or think there's some kind of superiority of one over the other in an absolute sense. Basically, the truth is that 1) in some ways they're not
all that different, but 2) in other ways they're
different enough to have different strengths and weaknesses. Both these things are true. Plus, so much depends on just how good the game is and well-designed it is overall. There are shitty RTwP implementations and there are shitty turn-based implementations, and brilliant implementations of both as well - and yes, it does have a lot to do with the quality of encounter design too, as many have said.
Another distinction as far as I can see it, is that the strengths of turn-based make it tend towards a board-game type of deal, where each encounter is a staged "chess match." In fact, if it's not like that, then it's annoying (again, if in turn-based you're having to give boring orders to most of your characters like "fire," then that's lost the point of turn-based). Whereas the strengths of RTwP make it more congenial to a design where you can have a more quasi-realistic form of exploration - the encounters are more like fights you're stumbling into in the course of exploration, rather than separate, staged, juicy chess matches. In that way, it can give more of a sense of being in a virtual world. Of course I'm painting this in terms of extremes, and the two forms can be closer than that, but that's kind of the tendency.