The threadripper is not targeted at gamers. It is targeted at people who make money from using their machines, these people can, therefore, afford to upgrade.
Consider a user who does video work. (most modern films and tv is filmed in 8k know) if this is in Raw format as it comes off the camera for a 90 min episode that is 6000 GB. Working on this data (tone mapping, cutting, etc) needs all this data to be fed in and out of the (CPU and or GPUs) so all these PCI lanes are there so you can have very fast access to the raw data and still have space for 2 or 4 full speed GPUs to do that work for you.
Forget games no game developer optimizes their games for 4 GPUs these days even Nvida have said that they dont realy want people to do more than 2GPUs in SLI.