"why does everyone seem to work with BiaB and export to DAW, completely skip and ignore the existence of RealBand?"

Because most DAWs can handle big audio / MIDI projects better.

With all arguments "for" RB I have seen, most "missing" things can be done in BIAB these days, as a lot of features were added in the past 3 years. As one prominent user said a few years back: Real Band should be kept "working" as a legacy product, focusing on BIAB and Plugin. I agree with that statement 100%.

MusicVillain,
I am curious, if you had a chance to change only one item in BIAB. What would that be in your opinion, to make most impact for the better?