Why? Uh, trophies, apparently. But it does mean that unless Sony issues a firmware update changing this, a PS4 will be useless once they shut down its online servers and its CMOS battery dies.
But when you examine the actual player numbers, the peak CCUs have typically remained below 10 for several years for these kind of titles.
I presume its the same for the PS3 - download and purchase activity must be essential minimal on that platform, and there are enough cheap second-hand disc versions of games floating around that being able to continue playing a treasured ancient title is not going to be a big problem.
Should’ve waited, clearly!