Here me out on this.
If Sony made already owned digital games free to stream, it would encourage a lot of people to transition to digital, which is something that would help Sony since they would get a higher cut of profits.
Also, seeing as that a $15 digital game is about the same price as a one month game rental on PS Now, Sony wouldn't be losing money with this. Since people generally don't play games again too much after the first month anyway, it's doubtful that the user would put any more load on their server than someone who rented the game.
This way, people who want to own the game and play it on their own time can purchase it digitally, while people who just want to try it out can rent it for cheaper.
Disc users will have to be left out, since not all PS Now devices have disc drives, but at least it will bring a lot more people into Sony's digital ecosystem, meaning more profits for them in the long run.
EDIT: It's not free, you still have to purchase the digital game . The digital acceptance rate is very low right now, and this would push people to buy digital. Most people have disc retail games, so they would still have to repurchase the game, which should more than make up the costs, as a $14.99 game is equivalent to 1 month of PS Now.
As an added benefit, users will be more likely to purchase brand new, $59.99 retail games digitally in the future, since they may be come usable on PS Now eventually, and that results in more profit fos Sony due to online distribution.
You're Gonna Carry That Weight.
Xbox One - PS4 - Wii U - PC










