For me it was five things:
1) No shutter lag.
2) I already had two film SLR's (Nikon F, and F3HP).
3) I already had some Nikon lenses.
4) Home digital darkrooms are far more advanced than film ones.
5) The insanely fast flash sync speed of my D70 (1/1000th second with RF triggers,
and 1/4000th second with wire. Too bad Nikon obsoleted this feature.

If I resist the urge to switch from my 18-200VR, I have a range of 10:1+, and no dust problem.