Why do you think Disney charges for this? mE is such a magical perk, it would be great if transportation was included as part of the cruise!
Disney started ME to deter guests from renting a car at MCO. If one has a car, they can easily spend a day at SW, USO, KSC, etc. If you're trapped with no wheels inside WDW, you're less likely to seeking outside transfers to visit other places. Therefore Disney gets 100% of your vacation $. All meals, souvenirs, etc.
Prior to ME, it was similar in cost to hire a transportation company to take you to WDW or rent a car. We always rented a car so we'd have the freedom to go where we wanted to.
With DCL, they already have your $. They're already providing all your food & entertainment. There's no incentive for them to get you to the port. They price themselves to be a little higher than their competition but also make it more convenient. Anyone who has dealt with the stupid shuttles with rental car companies knows, cramming all the bags for an entire family on a 7-nt cruise into the trunk of an Impala, waiting in the CASH line at tolls, refueling before drop off at MCO, etc. it's just not a very relaxing way to end a cruise. For larger groups it may be cheaper but to me if I've already spent so much to cruise DCL, I might as well let them deal with my bags.
If you fly home same day as debarkation on a participating airline, you may be able to use Onboard Check in: to have DCL check your bags the last night of the cruise. They also deliver your BPs right to your cabin. Then you don't see your bags til you get to your home airport. Just hop on & off the bus then head to your gate. So convenient.