I think you nailed it almost exactly. I won't say that they
...just trying to narrow the field by making the application process more tedious and daunting...
but they (people, designing the forms) do not particularly care about streamlining it and making it more inclusive for mature students students from "non-typical" backgrounds.
I do not want to say that Universities as a whole do not care. At some level, they very much do. Universities often have special people or even teams dedicated to improving access for "under-represented" groups of students. However, the activities of these accessibility teams, however excellent they are, rarely affect the practices of internal departments responsible for managing the application process: Admissions and HR. I have certainly came across the HR departments using the same forms for ~20+ years, some of which are quite bizarre. My favourite was perhaps when I applied to a University Lecturer post in the UK and was asked to produce the results of my GSCE exams, which are college-level exams in the UK, which I never had because I did not grow up in the UK. The web-site of this University proudly announced their international outlook; however, the HR processes did not recognise a possibility that anyone with non-UK education may ever apply for the post.