Maybe it's because I grew up with TNG, and TOS was more of a novelty for me, I just can't see TNG being rebooted on the big screen. It ran longer, was more successful, and featured more developed characters (IMO), but TOS is iconic because it started the whole thing. By the time TNG came along we had TOS, TAS, and four feature films featuring the original cast. I don't think TNG would ever be successful being completely rebooted. Maybe it's because I feel Star Trek as a concept works best on the small screen, despite having some very successful films.