Except you have to compete with all the other stores, it's the sole reason consoles exist so you don't have to. You are over thinking this.
Do you think Microsoft would release there Xbox exclusives on PC if it wasn't because of Windows?
The day you can play Forza or Gears of War on a Mac or Linux (and no streaming from Xcloud doesn't count) will be when what you suggesting might be true.
Well the answer is 'yes' if the monetary cost of doing business was the same. If they are moving their exclusives to steam in which Valve is taking a 30% cut of profits - then it doesn't matter that people are using windows, that is a 30% loss.
The only reason we don't see the games on Mac and Linux in native format is because
a) it's going to be costly to port
b) the drivers and APIs are not mature to run on _any_ linux or mac setup.
The likely main reason MS is willing to port to Windows PC is because it's cheap for them, everything runs on Direct X. You will see xCloud as their method of porting to platforms that are too challenging to reach natively.
The introduction of exclusives on PC does not indicate the death of consoles. Quite the opposite. It is an excellent feeder system that allows them to net additional profits with some side possibilities of netting some cross technologies. PC games also get the most coverage on streaming and eSports - so there are those net bonuses as well.
Lets be real; the cost of building a PC to equate to the power of PS5 and XSX will be tremendous. Anyone crushing out the math will promptly stay in console land. Only those who just have too much money to burn will be willing to pay for the hardware and the games to play on equal or better settings on PC. PC is good marketing for your titles as well as some additional profits.
And if you're forward looking about it; having Nvidia do DLSS modelling for your exclusives can't be a terrible idea either. Would be a useful thing to pay them for the model and back port it to console. AFAICS, nvidia currently does not have a competitor in the area that is competing to build up-resolution anti-aliasing NN models. Owning the processing power to do it is one thing (MS, Google, Amazon have it) experience, process, tools, talent and labour is another.
I'm in alignment with
@chris1515 ; I'd say in 4 years we might see PS5 exclusives on PC. It took MS a while, about 5 years, even though they announced in in 2016.