Back since the early days of WWF No Mercy, unlockables were aplenty. Legends, arenas, costumes, loading screens -- you name it. Players earned in-game currency and could use it to work towards these items. It was exciting to browse the catalogues, and felt rewarding to make purchases.
Unlockables never died, but this system has. More recently, players earn unlockables by simply playing through the game's modes. Though this encourages players to explore all aspects of the game, it is far less rewarding when you're forced to play through something you have no interest in.
On top of this, with developers trying to maximize profits, in-game unlockables just don't make as much sense as they once did. Why put something on a disc, when you can just release it a month later as DLC?
It's a shame. Give the fans what they want and bring back the incentives. I mean, who wouldn't want a Lita loading screen?