Because KiCad isn't stable enough for the professional world.
Also the interface is to much of a problem.
It's very different than all the other big/old professional programs out there.
Re-schooling/educating people is not only expensive, but it's also very difficult to convert over a couple of hundred designs into a new program.
And there is also a confidence issue. If you are not 100% confident about your skills in a new software program, the end result will show this (with sometimes major errors).
Plus KiCad used to have so very major bugs and extremely time consuming/typical nerdy approach (= to much programming and hassle involved)
That's why I voted for Diptrace before, it's much easier and intuitive to use than KiCad.
People pick it up much faster (based on research I did with several companies).