I wonder what the upsides are of hiring assistant professors instead of more experienced professors.
I am mostly interested in US universities and computer science departments.
- Their salaries are far lower. (The discrepancy varies by department, high in the physical sciences, low in economics and business.)
- In fields that receive startup packages, their startup packages are far lower.
- Many schools cannot hire a proven superstar, but they can take a gamble on a bright young scholar and help her develop into a superstar
- This doesn't apply in my department, but you could imagine that a disfunctional environment the senior faculty might like having junior faculty around to take advantage of: make them teach the big intro classes, do the unpleasant service work, etc.
- Junior faculty often bring new bleeding-edge skills that are hard to find in senior faculty.
- A range of career stages within a department creates long-term continuity.
I'm sure others can come up with a number of additional reasons.