The difference is, as many often say, CityWalk is sort of like an extension of the parks. That's Universal's chance to get promote their brand (NBC Grill Brew), give an immersive dining experience (Toothsome) or just provide other table service options for on-site guests (Antojitos, Vivo, Cowfish, etc).
Disney Springs is extremely disconnected from the parks and is also about 3-4 times the size. There's still plenty of experiences like what can be found at CityWalk (as far as originals) all over Disney property at their hotels and whatnot. Disney Springs is giving guests a different experience than that though and honestly, more times than not, it's for the better, especially on the restaurant side. Most of the mouse operated restaurants can be middling at best, but DS has a truly great lineup of restaurants and even their quick service places now is of higher quality.
Think about it this way - Is the pizza at PizzaRizzo what you would rather pay $10 for or would you rather have Blaze Pizza? The outside vendors do it better when it comes to Disney and food.
Disney actually bought Harley out of their lease because they wanted that prime spot. That store is doing gangbusters. They open up some stores here and there in DS, but my overall point is, they try to stay away from it unless it makes financial sense. Operating a huge building like this on their own would've been a big financial risk.