While I can't speak for certain I'd imagine it has to do with a variety of factors including cost, time, and game development goals. You have to remember that Gundam games are generally cheap production games made and are riding mostly on the fact they are Gundam, of course there are exceptions to this but that's what they are.
Other then that we can look at the games with familiar subject material and ask is there really a need to reanimate the famous scenes from the anime again? For example Pilots Locus on the Gamecube featured no cinematics at all and the game didn't lose anything from that because they wouldn't add anything new and would largely be familiar things we've seen multiple times. Other games like Lost War Chronicles are lacking in story generally and cinematics wouldn't add much. And then you have some like Rise From the Ashes which simply wouldn't fit into the game style at all.
The games are about the gameplay not about adding new fancy animation which fans can try to pick apart for scenes they've never seen or action not seen or something reanimated. The focus is probably on that instead of flash.
Which I agree, however every since the next generation gaming came out, it's all about the graphics now, which gameplay has taken a backseat. It is totally like you said the gameplay of it all, but when developers shows up a new game for example, it's usually a cutscene verses actual gameplay.
Now being that it's 2011 and shows from the past are being requipment toward 1080p I say, yes to reanimation in terms of gaming. I wish I could show it, but Youtube took it down, but they totally redid Amuro and Lalah's fight scene in a music video. Looks awesome.