Much has to do with frequency of doing the operation. The commercial trucker is backing into places every day. Each time is very similar. Into a tight but squared off spot. As long as he works with the side he can see, he knows he is safe. He does not have overhead stuff to think about.
The 35' 5er was my first experience with any trailer besides the homemade trailer for the mower. The backing is all self taught. We actually prefer a back in to a pull through site. Can't say it is always easy & not always pretty but it is always done under the direction of the DW via the FSR radios or simple hand signals. The operation never looks like 'so you think you can dance'. There are no screaming voices that can be heard all over the CG. She gives direction on where she wants the trailer to go. I follow directions.
When things go wrong it is often much easier to go forward & start again than to try & fix it with a bunch of backwards & forwarding only moving a few feet.
The only way to get good at reversing is to do it frequently & do it into challenging sites.