There is a massive difference in terms of the sheer numbers of slow moving family attractions at WDW compared to Uni. To wit:
WDW
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POTC
Jungle Cruise
HM
PPF
IASW
TLM
Pooh
Buzz
Peoplemover
Railroad
SSE
Nemo
Imagination
Energy
Mexico
Maelstrom
GMR
TSMM
You could potentially add the safari (it's a bit bumpy though), Backlot Tour and the monorail (it's transport, but also sort of an attraction) to this list.
Meanwhile....
Uni
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ET
Disaster
MiB
Cat in the Hat
High in the Sky
The sheer difference in numbers is sizable. I'm not putting down Uni, as I perfectly enjoy going there. and many of their rides are fantastic. But there is a certain segment of theme park goers -- a segment that Disney has captured very well -- that is not looking for "thrills" but wants numerous immersive rides where the experience is the goal, not the movement of the vehicle. I'm sensative to this because my dad is that type of person and he hates ammusement parks, but loves Disney. My parents spend a week at Uni over this past summer and, while he thought it was fine, my father felt Uni didn't have that much that interested him and much prefers going to Disney. There's a certain type of ride that made him enthralled at Disney; Uni, at this point, doesn't have nearly as many of them.