Not everyone stays on property due to incentives.
The resorts are generally nice and have interesting themes. I personally enjoy the atmosphere of Disney resorts. I enjoy walking around the lake at Coronado Springs and the swimming pool features a large temple. Port Orleans lets one experience a Disney interpretation of New Orleans, which is more interesting than a generic offsite hotel.
Staying in the bubble means not having to deal with driving or using a hotel shuttle with a strict schedule. Anything one wants to do in WDW can be accessed by internal transportation. The buses run every 20 minutes so there's no need to fret about a schedule. Taking a boat to Disney Springs is certainly more fun than driving your rental car from the Super 8 down the road.
On my last trip I avoided Early Magic Hours, I just don't find them worth the hassle. I did two Evening Magic Hours over the course of a week. Magical Express was great, but I only used it one way due to staying at Universal after Disney.
The few perks I took advantage of were fine, but they weren't the only factor in my decision to stay on property. If I was assessing from a cost benefit perspective they hardly justified paying Disney prices on their own.
WDW is a vacation environment beyond the theme parks, and staying in the bubble can simply be a more "magical" experience.