I've already given you my Reason #21 - Why I Like Published Material. Here is another reason why I like them. They keep a DM honest. As a campaign goes on longer and longer, a DM begins to adapt to what the players bring to the game. If they always fly as they move down a corridor in order to avoid any potential traps, I will have the trip wire be placed at flight height. If they always spike shut a door after entering, I create doors that are soft and break when spiked. If the thief always stands on the right side of a potentially trapped door, I make sure to place the trap on the right side of the door. If they like to carry lots of flasks of oil, I make sure my monsters use fire against them.
Of course, this works the other way as well. If I put a stone wall in front of the character's progress, I also make sure they have a means at their disposal that will allow them to bypass that wall. I do not throw a level 25 monster at a level 2 party, unless I also provide a means for their escape.
Even when I don't do it consciously, there are times while creating my own adventures that I alter what the characters encounter based on my knowledge of what the players and their characters are capable of. Using a published module allows for me to run an adventure that was created without prior knowledge of the players and their characters. The characters will then run into things that may be below or above their expertise. If its below then the players can feel more powerful than I would normally allow them; if its above then the world feels more "realistic" and less contrived.
When running a published adventure my personal biases are not part of the equation.