People don't want to admit that you can be pretty bad at CS and still get by. This isn't unique to CS. There are plenty of people slipping through the cracks in all fields and disciplines.
It's especially easy to do in this field, because there can be a strong disconnect between the business side and the tech side. Most everyone on here can name at least one person they've worked with that created more work than they completed. It would have literally made better economic sense to have them watch movies all day at work rather than mangle the code base.