I am currently doing my first postdoc in mathematics and I noticed that when it comes to hiring for tenure-track assistant professor positions, some universities prefer to hire people with a single postdoc, while other universities (for ex. most places in the UK) prefer to hire someone with 4 or 5 years of postdocs (2,3 or more).
What are some reasons for the hiring committees to prefer more inexperienced candidates and what determines whether a university belongs to the first group or to the second?