Why does Wizards of the Coast print terrible MTG cards?
I already posted a link to Maro's article, but here's his summary:


By definition, some bad cards have to exist. (The most important reason.)
Some cards are “bad” because they aren’t meant for you.
Some cards are “bad” because they’re designed for a less advanced player.
Some cards are “bad” because the right deck for them doesn’t exist yet.
“Bad” cards reward the more skilled player.
Some players enjoy discovering good “bad” cards.
Some “bad” cards are simply R&amp;D goofing up.


I agree with his "most important reason" very strongly.  If all cards were created equal or almost-equal, then skill-intensive deckbuilding formats such as draft would come down to the luck of the draw, rather than card-analysis skills, a lot more often than they should.