My favorite people are those who drive giant SUVs with huge tires lifted way off the ground who do this and also slow down to 2MPH to go over train tracks.

At least up north around where I live manhole covers are often also either holes or bumps in the road due to things shifting around from the freeze/thaw cycles. Basically potholes with a purpose. Hitting bumps is bad for your car, so that's a pretty good reason to avoid them. Though I'd never swerve around a bump if I was going to come close to someone else, since that's much more dangerous.

Same reason I don’t let my foot hang out from the covers. Also that icky thunk thunk.

As someone who opens them regularly, because so many of the chimneys are collapsing and I regularly wonder how some haven't caved in yet.

Because I drive the same way every day. I know which ones to avoid and which ones are fine. I also have to pay to do maintenance on my car. If I can move the steering wheel a few inches for certain covers rather than spend a weekend replacing suspension, I'll do that.

It's fun to do on a motorcycle.

After freezing temperatures, construction, and deferred maintenance, manhole covers can be a damaging obstruction

My car is only two years old, and the one time it needed work …. I hit one of the smaller pieces of road infrastructure - a gas valve maybe. But the pavement was broken up around it so it was a deep hole with a sharp metal edge. It destroyed my tire, a damn expensive tire

Edit to add: for my older car I just had to spend $1,500 replacing a control arm and ball joint. While there’s no way to identify a specific cause, trying to avoid obstructions is a possibility I can control

In my city, they just keep paving over the old asphalt, so the manhole covers are like 6 inches deep in some places. Hitting one of those in my sedan is not pleasant.