I am not sure I understand the difference. If all you do is sleep and shower at WDW as well, then why stay on property? Also if you did stay on property (for example, the Grand Californian) at
Disneyland, chances are you would branch out from your sleeping/showering schedule. You might go back to your room mid-day, and lounge around the Grand Californain pool. It really is a lovely place to spend some time recovering from the parks. You might spend some time sitting in the lobby at night with a hot chocolate by the fire. You might find you enjoy the who experience of staying on property to enhance the experience, as you do at WDW.
Anaheim itself is not a vacation destination, so when you leave the property area it is often not that nice.
I know people will never feel the need to spend the money to stay on property and I get that. I just don't get why some say they only stay at the resort at WDW, but Disneyland isn't worth it?