Springs has its share of problems from time-to-time but I think the style and setup of it these days is more towards "mature" (with younger people in tow) along with the drama club kids (which if you knew me, you'd know is a loving remark and not a knock) where Citywalk feels like Times Square at night - totally different vibe with a much more lively crowd.
I haven't done HHN in years due to a young one but when I went, they used to advertise that our ticket would also get us into the clubs in Citywalk for free. I never understood why someone would leave a hard ticket event like HHN early to go to the clubs there but thinking about it, the audience for HHN is a lot more likely to hit up those clubs after than the ones at MNSSHP.
The Universal stuff all the way around is geared more towards young adults looking for slightly edgier and less kid-friendly stuff and frankly, if I were a teen in Orlando, Citywalk would look a lot more fun to me so I get why they would have a little more trouble than Disney with locals - especially with the demise of PI.
I never did PI when it was ticketed and spent very little time there after
* but I can see how getting rid of it probably shed Disney a ton of headaches.
*If you're curious what I looked like when I was younger, just go to https://www.thesaurus.com, type in the word "cool" and then scroll down to the antonyms section. You'll se a picture of me from my early twenties which is still pretty much how I look today only more out of shape and with less hair.