Microsoft was opting out of crossplay before the PS3 was even released

It's not like the PS2 had much of an online service to interop with anyways--it was mostly run by the publishers, so I'm not sure what you're trying to imply here. PS3 is where any semblance of a true Xbox Live equivalent appeared on Playstation platforms, and Microsoft's resistance to allow cross-play based on security concerns was later proven at least not overly-paranoid during the massive PS3 hack that took the service down for a month while Sony tried to figure out how to unfuck their shit.

These days the environment is a lot different--both platforms have mature online services and gamers now more than ever are demanding cross-play as "games as a service" continues to become more prominent and the lines between platforms blur even more. Nobody wants to re-purchase cosmetics on different platforms, for example.