I used to think that. What will it cost to rent and gas a car? $20/day ($140/week with fees) sounds reasonable. What does it cost to part at Disney? $14. Now assume your offsite hotel charges $10 (parking or resort fee). There goes $45 per day. Add perks like EMH.
The numbers change as you upscale your hotel. $400-$500 for a Disney deluxe. Maybe $100 for an offsite resort. Maybe $200 for the Swan/Dolpin.
OP isn't renting a car. So you aren't really comparing, but....
This weekend I am staying at the Fairfield Inn.. $75 a nights for three nights with the 4th night free. My other options were $100 plus a night for a value.
Hmm. $400 vs. $225 for the 4 nights.
Rental car let's use the $20, parking $14 resort fee zero.
So my extra costs are say $50 a day.
So now I am up to $425 for the stay. BUT...
I get free breakfast, interior corridors, a rewards program that lets me earn points for FREE nights on future visits, more space, a king bed without paying extra. So is the $25 savings worth it. For a hotel that offers less? .

Sorry but putting a giant Buzz Lightyear does not get away from the fact that a Disney value is an exterior corridor hotel that wouldn't meet the standard for most hotels you might stay in. Plop that thing on I drive and it's $49.99 a night LOL! My company travel policy wouldn't even approve a Disney hotel (no exterior corridor hotels are allowed due to security concerns!)
Plus I have access to much better priced/quality food at an offsite hotel.
And as you go up the "chain' the discrepancies between Disney and off site get greater not less.
Disney hotels have become "pay more, receive less" Free Transport is only worth so much.