As already said, high aspect ratios (high wingspan) reduces induced drag (mostly present at high CL), high wingsweep reduces transsonic drag.
So if you want to fly fast (for jet powered aircraft) you choose some ammount of wingsweep. This reduces your CL max, because at high CL (high suction peaks on the wings upper surface) some outbound spanwise airflow is induced on the upper surface, creating serious problems.
So if you have to accept lower CL due to the wingsweep, high aspect ratio is not so important.
On the other hand the wings torsional stiffness gets more important for high wingsweep because of aileron reversal effects. And higher aspect ratio means lower torsional stiffness.
´I assume that most turboprop airliners don’t have swept wings´
right, but there are some exceptions, for example the
TU-114