Well, CPUs are not very relevant for games in general, with very few exceptions. So broadwell single threat performance (that's what Zen is currently compared to) is totally sufficient for most games and the mobo and CPU might be much cheaper. Remember that Intel boards are also more expensive too because Intel forced their board partners to make the pins for the socket.
Vega 10 has some really great architectural stuff btw. fp16 double performance for example (something NVidia promised but didn't deliver). NVidia has better marketing (as seen in these forums) but AMD certainly has better architecture in the GPU department.