The PS2 remasters that are being made available on the PS4 run for around $15. That price may seem a little steep, considering they only receive a slight boost in appearance and mostly only add trophy support to the original game. Apparently, adding trophy support takes quite a bit of work, though.
Tim Lindquist, Senior Technical Project Manager at PlayStation, has stated that even deciding which trophies will go in the game is a task that takes 1-2 weeks. Actually programming the trophies into the game can take a month and then testing and QA can take an additional month or two on top of that. Of all the currently available PS2 emulations running on PS4, he says that Dark Cloud was the hardest to program.
Lindquist also states that gamers should expect updated PS2 games regularly and Sony is currently looking for suggestions about which games to work on next.
Source: Gamingbolt