Iowa city doesn't even run buses on the weekends/holidays. I really don't think this should be a model for real urban centers
Most of the routes run Monday thru Saturday. Schedules are something that are easily changed to support demand.
As to why Iowa City doesn't run on Sundays and Federal Holidays:
The University is about half the population of the city. The University runs a separate "Cambus" system[1] (that the community can also use) and after-hours routes for students[2].
We're also still in relatively early days of finding out how Iowa City residents use public transit when there's no barrier. For instance, they stopped running the downtown shuttle and reduced the number of stops downtown[3] because downtown is relatively dense, walkable, and student-heavy (i.e. mostly young, healthy, ambulatory people) and served by the University.
There's also a growing interest in adding service to nearby towns and adding Sunday service, even if it's in a limited capacity.
1: https://transportation.uiowa.edu/cambus/cambus-service-calen... 2: https://safety.uiowa.edu/nite-ride 3: https://www.icgov.org/Home/Components/News/News/2165/390
If I want to look at succesful systems, IDGAF where they are, but how they operate.
Let's just look at some basic comparison between Iowa City and my own city of the same population (mine is somewhat larger in metro city):
about 1.05 million trips
about 50.1 million trips
Its not even close. Why would you look at some tiny US city that doesn't even have actually good results if you compare it to anybody even halfway competent. Why not look for evidence in systems that are better by LITERALLY EVERY METRIC?
That's the basic issue with looking to the US cities for evidence. Their baseline is so pathetic that 'improvements' isn't really that significant.
So maybe its time to start giving a fuck, and not cherry-picking examples to confirm your bias. Actually learn from the systems that achieve the best results.