Seems I'm pretty much on the same page as the majority of ENWorld DMs in prefering to write my own stuff. The reasons for this vary a bit, but one thing seem to be recurring:
If you write your own material, you are intimately familiar with it. This makes it easier to do stuff on the fly when you don't have to follow somebody elses resipe (in other words, you don't have to railroad the PCs into following the script).
Also, making adventures is fun!
For me, there's a third reason and I'm surprised nobody else has mentioned it. Maybe I shouldn't either, for it might just possibly offend some of the regulars here. Specifically, the ones who actually have published adventures themselves. So before I voice my third reason for writing my own adventures, let me just go on the record as saying that I mean no disrespect and the following is certainly not meant as criticism of adventure-authors! This is just me talking of my own likes and dislikes.
Ok, here goes: I find running a store-bought adventure is very, very boring! Admittedly, I've only ever made one serious attempt at it (RttToEE). This was in a fit of desperation after having 4 -four- campaigns end in TPK during a total of 5 -five- sessions...
(Yeah, I know how that sounds! Sounds like I shouldn't be allowed to make a single encounter myself, doesn't it? I can only hope you believe me when I say it wasn't my fault! It was just a long streak of extremely "lucky" rolls from me and nothing but bad rolls from the players (all rolls made in the open in our group). It was like I could never roll lower than 17 and the players never higher than 4! 2 lvl 1 orc warriors against 4 (fully healed and rested!) lvl 2 PCs and it's a TPK, and before a single PC got to make a single action... It just shouldn't be possible.)
So I was rather burned out in the coming-up-with-new-campaign-ideas department, RttToEE was just out and I'm a fan of Monte's work, so I decided to give it try. Great story, cool characters, nasty monsters (except the rather silly giant toad)... Yet I was bored stiff. It felt like I wasn't even part of the game, my job was reduced to being the guy who looks up things in the book to see what happens next, and it was the least fun gaming experinece I've ever had. I had been looking forward to a break of sorts, to not having to come up with new stuff for every session, but it was huge disappointment and I've stuck to writing my own adventures ever since.
Am I alone in this or have others felt the same way, trying to run published adventures?
Spoiler! The RttToEE campaign also ended with a TPK, in the very first session. The PCs had been scouting around the orcish base, killing a few orc guards. They then decided to withdraw and rest for the night. They built a camp, complete with campfire, less than a mile from the orc stronghold. They talked about camping further away, but figured the orcs wouldn't be able to track them anyway. Completely forgetting about the kennels full of dogs the orcs had...
We started over; with each player playing a friend or relative of their original character, coming to look for the last party. Those characters lasted all of 3 sessions. By then I was frankly relieved to see yet another TPK, since it meant I could start a new campaign of my own design.