Progression is becoming one of the necessary ingredients for modern games. Sure, games of the past had a sense of progression as well, but much of the emphasis was on personal challenges and speed of completion in games such as Mario Bros., Contra, Castlevania and Megaman.
However, a large number of recent games are keeping players coming back with levels, rankings, unlocks, achievements and more. Even Castlevania games have adopted levels and unlocks.
So why are there more progression mechanics in games now, if games of the past were just as fun for their time?