PC has similar architecture to the PS4 and X1 so I guess it doesn't take much effort to port it over. Not to mention we don't know when GT7 will be out.

On X1 and PS4 they actually have a hope of making money on their investment. The Wii U port is an act of charity for us suffering owners.

One thing to keep in mind is that the game's already paid for and is being made with a significantly smaller budget than most games these days, it doesn't need to sell gangbusters to turn a profit.

I'm not certain of the timeline but I'm fairly sure this game was announced for the Wii U before its sales woes started, the decision to include XB1/PS4 versions is more recent. Given the similarities between PS4/XB1 and PC architecture, porting shouldn't be an expensive endeavour and might help to make up for the small Wii U user base.

I'm certain the developers are counting on a lack of competition on the Wii U and established audiences on the XB1/PS4. Again, it doesn't need to appeal to every Forza or GT fan, given the low development cost, just a percentage of them.

I would say the opposite. PS4/Xbox One and PC versions will be the only ones that are going to show the full potential of the game. Even if the gameplay isn't top notch it would still be a reason to grab it. Forza 5 was a bit limited in content and GT7 is not even announced, so no or just barely competition.

On PS3 and 360 it would've been one of many racers and the WiiU version should be the lowest selling one anyway, even if the last gen versions weren't cancelled.

Development for ps4 and Xbox one versions are branched from the PC version, the wiiu version is going to need the most effort and time spent on it.
As such rather than asking why they're bothering with ps4 and xbone, you should just be glad there will be a wiiu version.

P.s. while it would be against forza and gt on ps4/xb1, its against first party and third party hating Nintendo fans on the wiiu, I'd argue that that's more of an issue than forza or gt.

Its PC built game that will easily port to the PS4/X1 the only thing that mkes no sesne is the wiiu version, it would if they were still making PS3/360 versions.

Wiiu also has ninetendo owners that for years shit on Sims and how boring they are, this will flop on the Wiiu.  X1 and PS owneras are used to and histroically support realistic racers quite well, nintendo fans flat out hate them.  Though iv seem plenty hypocrisy from them about sims and PCars.  

Simply put they need as many sales as possible. Racing fans are likely to buy Project CARS on the X1/PS4 regardless. They are more open then "certain" customers and will happily play racers outside Forza and GT. See NFS Shift and Dirt to a degree. On a technical level porting to the X1/PS4 must be relatively easy considering how they resemble mid range PC configs. Not much scaling or cutbacks required though I expect resolutiongate might feature >_>