This is honestly one of the biggest things that makes the parks a worse experience now -- the Magic Kingdom and especially Hollywood Studios have taken significant hits from this shift. DAK was mainly built/developed after the shift, so it didn't really change, and EPCOT has managed to keep some uniqueness due to the World Showcase.
Tastes regarding attractions etc. can vary wildly from person to person, but I'd guess the vast majority of visitors aren't excited that the stores throughout the parks tend to sell variations of the same merchandise (with a few exceptions, especially when that merchandise is also generally available at World of Disney and/or the resort gift stores. It means there's little reason to spend much time looking in the different stores in the parks, which has knock on effects for capacity and crowding.