Intel usually discontinues support for vs versions which Microsoft no longer supports. You could say it's a money matter, no feasible increase in fees could cover the increased less productive work. If you want a compiler independent of vs you know where it's available.
I think Intel has been disappointed in the market share gained by Intel c++ but mingw et al seem to have a miniscule share of the market of interest to intel. You've probably noticed the effort intel has put into improving Windows Mac and linux compilers which compete to some extent.