I understand you wanted others to give their reasons.
I disagree with one of your reasons, at least the way you worded it. A person who's planning on ending their trip at their resort doesn't gain much with a rental car vs DME. Allowing enough time to gas up and return your rental car offsets most of the time savings.
People rent a car because they want to do stuff offsite (yes we can list lots of stuff), because they're doing non-theme park "stuff" at Disney (yes we can list all the "stuff" including visiting other resorts) where bus service is poor or because they have "issues" with Disney buses (yes we can list the "issues" including not wanting to wait, wanted to ensure they don't have to stand, etc).
Likewise there are only a few reasons why people don't rent a car. Some people can't easily rent a car (list the reasons but basically no license, horrible driving record, huge underage surcharges), prefer not to drive on vacation, prefer not to spend the money or aren't planning on doing anything that requires a car.
edited to add:
What guests have virtually no reason to rent a car? Guests who are staying at an EPCOT resort, who are on a meal plan and who plan on spending all (or almost) all their time in their resort, EPCOT and DHS.
Which guests should almost always rent a car for their entire stay? Guests staying offsite. Almost all offsite properties have limited to poor bus service.
Which guests should rent a car for at least part of their trip? Guests planning a trip to KSC, Bush Gardens, Clearwater Beach and maybe Universal.
Otherwise there isn't a "correct" answer. People need to balance the pros and cons.
The weekly cost to rent a car used to only a few dollars more then the cost of car service transfers. Some of the current rental rates are pretty high. Some people might consider using taxis to supplement Disney transportation.
I'll give you a positive reason, that can become a negative. A car may make it too easy to go offiste. I have outlet malls near my home. Souvenirs are cheaper in the Character stores in the outlet malls and in
Walmart. Many of us wind up spending more dollars when we drive offsite. We get more "stuff" but more then we need or really want.