shows wonder why they got cancelled?
mine are:
forever
journey man
john doe
seven days
moon light
numbers
the mentalist
early edition
quantum leap

comedies
step by step
family matters
the wonder years
family ties

Gilligan's Island
Green Acres
Get Smart
Star Trek '66

Though to be honest I know why these shows were cancelled - it was the networks' poor judgement in the late '60s/early '70s about what shows deserved to stay on the air. What's worse is they didn't even give these series enough notice to film closing "finale" episodes.

shows wonder why they got cancelled?
mine are:
forever
journey man
john doe
seven days
moon light
numbers
the mentalist
early edition
quantum leap

comedies
step by step
family matters
the wonder years
family ties

Forever, John Doe and Moonlight were cancelled because they weren't doing well in the ratings. or because the networks airing them felt they had no future.

The Mentalist, Quantum Leap, Numbers, Step By Step, Family Matters, The Wonder Years and Family Ties had all run for a really long time and had long past their creative peaks. They likely weren't seen by the studio or network as being shows that would continue to be profitable. In some cases like Family Ties or The Mentalist, there was probably a decision made by the executive producers to end the show.