Due to the fact that you need little skill or ability to make a PC game many of the millions of games are, quite frankly, trash. Yes, the measurement of platform value would be the number of good games, but while PC has so many more games, console has more GOOD games.
Platform-exclusive content and games are generally done as a marketing platform to draw players to one platform instead of another, like the Xbox vs. Playstation platforms. Xbox has games like Halo and Forza to pull players to them while Playstation has Gran Turismo and Infamous.
Consoles are purpose built, much cheaper and offer an at least equal experience. Additionally you can get almost all of the most popular games on console platforms, whereas PC lacks many of these titles. Additionally, most of the greatest people in the industry devote their time to console.