First is the visibility of these pull-outs is often very poor. You'll be driving through long winding roads and then all of the sudden the pull-out appears. In an RV, you can't just slam on the breaks and swerve into the pullout, ESPECIALLY if you're going downhill.
Second, often times (in the USA at least), these pull-outs have rough terrain going in an and out of them. There will be a little bump or uneven ground that most vehicles wouldn't mind hitting every now and then, but in my rig, that causes the whole thing to sway back and forth (Class-C built on a Mercedes Sprinter). I REALLY need to upgrade the suspension.
Third is time. Since I'm slower than everyone else, people tend to pile up behind me pretty quickly. Pulling into the pull-out, coming to a complete stop, waiting for everyone to pass, then getting back up to speed takes a long time. If I did this every time there was a car behind me, it would take forever. So, I tend to wait until there's more than a few cars behind me before pulling off.
Fourth is my wife. She says I have "overly-considerate disorder" and I need to make our safety #1 and stop caring about other people so damn much.