Because one of the cards diehard Sony fanboys want to play is the 'I have Horizon Dawn - you don't! Nyah nyah nyahanyah nyah!'. These news ruin it.
For me, there is a lot more to it than this.
+ Sony (and other console manufacturers) want you to get onto their platform.
+ In order to get you onto their platform, they need to provide a great gaming experience.
+ One way to do this is to create unique games and that aren't found elsewhere.
+ Therefore, we get Uncharted, God of War, Bloodbourne, Horizon Zero Dawn, The Last of Us, Gravity Rush, etc.
Now consider what would happen if we started throwing all the games onto every available platform. After a few years, there's not going to be much point in creating something special and unique, because you're not trying to draw gamers to one place anymore.
You're probably reading the above and thinking, but if you create something unique and put it out there lots of gamers will buy it and it'll be a great success, bringing in a lot of money in the process.
Yes, that's true. But there's something else one needs to consider: creating something unique is a massive, massive financial risk; just look at the way Hollywood keeps throwing out the remakes and sequels. It's because in the main it's safer than trying something new. Companies have and do go bankrupt in their quest to deliver something special and ultimately failing hard. Sony actually bankroll a lot of games that are risky but just may well pay off by making gamers buy a PlayStation to play them.
In short: this industry has been built on platform exclusives and needs to remain that way.