Gonzaga plays a schedule with 14 easy conference wins a year. They get a one or two seed based on an inflated record and have to beat one very average team to get to the sweet sixteen. They join the B12, and get exposed to high level competition night in and night out, they’re losing 8-10 games a year right from the jump.
Lower seeds into the tournament means earlier losses. Now they start to look like just another program, their recruiting suffers, 8-10 losses turn into 10-14 losses, now any big time recruiting is wondering why they would want to go to a small school in the middle of nowhere with no close rival schools. Few retires or leaves and now we have a team going 10-20 or worse.