Can you elaborate? Genuinely interested. ETA: Logistical situation or financial situation? Because the price point from Disney seems to cram too many guests into the system at the expense of guest satisfaction in the interest of raising as much short term cash as possible.
A few basic principles..
Express Pass is not intended to be a 'for everyone' solution - It is by design intended to be used only by a limited subset of the attendance. Contrast this with Fastpass which was intended to be used by all of your guests. Genie+ is still an 'everyone' product - it's not priced nor limited to be a finite audience like EP.
Utilization/Crowd Levels - Disney parks have trended to be more loaded than Uni outside peak periods. This means there is a great demand for such a line-skip/reservation system and greater expectation 'something needs to be available' all the time at Disney. The majority of time, the majority of Uni guests don't have EP at all and are fine. Meanwhile, Disney crowds are in meltdown if there is no FP available.
ExpressPass does not exist solely as that premium priced service - They have a large userbase who is gifted access to the service via their hotel booking. So its more challenging to qualify how many are actually buying the adhoc packages. So 'what people pay' is kinda nebulous. Uni has clearly made enough money from the last minute buyers to make it worth keep marketing it. I see it as capitalizing on a small % of customers that are willing to basically 'pay anything' to bypass lines. I highly doubt you see many people buying adhoc EP for more than 2-3 days in a trip. Disney has far more hotel rooms than Uni.. so if you did a hotel bundle at Disney you couldn't just use the simple 'deluxe' tier distinction.
The number of days you are on property - Disney trips tend to be far longer on avg than Uni. If it's a product you expect people to use every day, you have to consider someone's total investment expected. A several hundred dollar price point per day is more approachable if you only need to do it 1-3 times.. if you generally expect to use it 5 or more days.. the price point becomes far more problematic.
So to sum up.. EP is designed and priced to be used only for a subset of your population. In addition, Uni can get by without NEEDING to give all their users a line-skip because of their park crowd levels in general. Obviously as Uni grows in popularity that dynamic changes a bit.. but hasn't reached that saturation yet where Uni is a 'Expresspass or don't go' experience.
The fundamental difference in how much capacity is needed to feed the line-skip machine is a huge part of why the systems aren't directly inter-changable.
Yes, Disney could just turn around and charge $200/person for a line-skip service and say "ok, its only going to be for 5% of our visitors". But if 95% of visitors are left out.. either due to capacity or or financial accessibility then you are abandoning the majority of your userbase.. and their need hasn't diminished.