so people can experiment with them and for archiving. same as why 3.60 encrypted games are uploaded online and 3.55 games before them.
As of now there is no way of playing PSX or PS2 backups (or PSN classics downloads) thats been released apart from a psx emulator but its very buggy and has little support.. use the search function for details.
yes it is possible don't let ppl mislead you, if you have a launch model just buy swap magic put the ps2 iso on a pen drive /external hdd load the the game and enjoy.