This.

As a DIYer for 8 years 'ish, mudding drywall is an art. Where it might take me 4 or 5 (or 6) to get a good finish on joints or corners, it might take a pro 1 or 2 coats and very minimal if not none sanding in between. Primer and 2 coats of paint won't fill in imperfections greater then an 1/16th in diameter so if you have a lot of imperfections, you'll see it in the finished product.

Let's not even discuss mudding ceilings. The amount of upper body strength needed is amazing, let alone good balance on a ladder.

Yup, just because something can be done by a "grunt" does not mean that there isn't skill required to do it well. My girlfriend just moved into a house that can be best described as "the victim of a flip" and you can immediately see the difference between work was done by a pro and someone who is just banging on the keys.