Probably not enough PC gaming customers to warrant hiring a different developer to port the game, considering they can't sync its release with the console versions. After High Voltage Games broke every single WBIE property they've touched, WBIE probably figured it was best to just turn their backs on PC gamers and leave it to the larger console customer base with fewer customization options and hardware configuration headaches.

Yup, upon hearing this news a friend of mine said "not supporting PC is a mistake"... confused i suggested to him that the numbers probably don't work out in PC's favor, the PC ports of fighting games probably only just break even or make small profits but that's a guess. Arc continue their PC port spree, Koihime Enbu seems to be well received and there are rumblings that Tekken 7 could be possible, it makes me feel like the fighting game market on PC could be growing but it's already a smaller genre than others so it's hard to tell.
Regardless of the budgets and profits, the ports in general need to increase in quality... and god damn it Tekken 7 needs to come to PC .

The demand will always be there, but the real question is who is developing it for PC? How many options are you going to provide for PC gamers? How many configurations will you support? Which controller input types do you support? And when will the PC version be released? Will it be released soon enough that those who want the game won't already have it on console? Will it be a synced release with consoles? How about timed DLC exclusives? Is that a thing? Will PC gamers get the same content at the same time?

Most of the time, the effort simply isn't worth it to WBIE, who would prefer to toy with their business practices on a simpler and larger market on console. What I don't understand is why WBIE contracted out to High Voltage Software to port console games to PC. It absolutely doesn't make any sense, when High Voltage's wiki doesn't even show a whole lot of experience releasing PC games before WBIE signed them on. If anything they seem better at doing console and mobile development, with one exception being a VR game that's coming later. And even if WBIE asked High Voltage to port Injustice 2, they'd probably say they're busy with VR. And instead of finding an ACTUAL PC games developer, WBIE figured it's too much work and expect us to just get it on console. They were never fans of PCs anyway.