wouldn't the qualifying session on saturdays be more exciting for the viewers & spectators if there was not over five hours of free practice sessions in the prior 24 hours?
that would make qualifying very unpredictable and make for great viewing - wouldn't it?
the drivers can walk the track, they can study maps, videos, virtual reality, etc, but there's nothing like driving the circuit to establish how the track cambers run, where the braking points are and how fast it's possible to actually drive the track.
most of the tracks introduce "improvements" every year, so the tracks aren't necessarily the same year on year. without the practice sessions, the drivers would have to be a lot more cautious.