Quite possibly specialisation: a palette for every taste. I have a Russian friend living and working in Beijing. He uses Provia 100 almost all the time now with a very occasional smattering of Velvia 50 (running through Hasselblads). Another correspondent, in Tasmania, Australia, uses only Velvia 50 in 4x5 (he is presently in Norway so waiting until his return, probably unawares of Fujifilm's decision...).
Conversely, I know and use more Velvia 50 and 100F better than (or like) Provia 100. Maybe we can surmise that at least Fuji is catering for a niche market with different tastes where photographers use more of one film, less of others. But you can see this doesn't explain how Velvia 50 can hit the skids in the intrinsically beautiful and unbeatable 4x5 format. It reads so unimaginable and difficult to accept.
Velvia 100 rated at EI80 approximates RVP50 in appearance. For me I didn't quite warm to its (100) fragile whites. 100F is a bit gaudy but is a definitely good choice for rainforests where it picks out subtle hues that are zealously slaughtered by RVP 50. I have seen only 4 trannies of 100F in the 4x5 form and initially mistook them for RVP50 being so well exposed and lucid. The telltale was the mustard-yellow overtures and subdued greens, even under polarisation.