Channels like nickelodeon and cartoon network are all intended to appeal to children-not teenagers, adults etc.
Ofc our opinions of these shows will be quite different to the younger generation. When they grow up, they'll look at the new shows airing on these channels and think "What's wrong with TV now days?". These TV shows are meant to amuse young children-Not us. The shows we saw as children will stick with us considering we grew up with them. This gives us the illusion that these shows were somehow better than the shows which currently air on TV. I honestly don't believe that shows have decreased in standards. The only thing that has changed is us. We have matured and these shows simply aren't enough to amuse us. Face the facts- you are not a child anymore.