ND has had maybe two national championship appearances/quality seasons in the last 25 years.
ND is not an easy place to recruit any longer -- the built in advantages ND enjoyed for most of the 20th century are long gone and the recruiting results for most of the 21st century have bared that out.
ND believes in the idea that college football is true amateurism -- where program's who are favored to win national championships year in and year out have publicly held that belief but privately have turned their football program into an NFL like business.
ND is way behind the first tier when it comes to attracting/securing commitments from the nations best prospects -- a lot of it is a result of their own self handicap (archaic policies as it relates to admissions, and eligibility; archaic beliefs that college football programs can win at the highest level while still providing a real education for their athletes, etc. etc. etc.)
Sadly the fan base is still in denial as well which only perpetuates the mediocrity.