Because so far I just can't see react as the best/simplest approach to dragging REST[1] apps into the world of GUI COD(Code on Demand)[1] apps. Vue seems to strike a much more elegant balance, for example.
Especially in terms of life-cycle - I can't say I'd look forward to maintaining most complicated js stacks for say five years - with a horde of (rapidly evolving) dependecies, and often a plethora of build tools/steps that in general all do some rather simple, but incompatible source-to-source translation (templates to html, some js dialect to another, scss to css).
Vue certainly doesn't fix all of that - but it seems a bit more consistent and simple IMNHO.
But maybe it's just me. It'd be interesting to hear if anyone's actually made the jump from "react in anger" to "vue in anger" - or vice-versa?
[1] http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm