Is that a lot of the reason that things get better is that the parents stay home and focus only on parenting for that week or whatever that she's there.

One of the reasons that training animals (dogs and horses in my case) is far easier for me is because when I'm working with a horse, for example, I am completely focused on him for the hour or so I'm working with him. No one calls me in the middle of an equine temper tantrum and expects to have a conversation with me. I'm not trying to do my taxes while I'm teaching a young horse to lead. When I'm done I put him away and he's out in a field for 23 hours (say) before I start again.

On the other hand, my toddler was with me pretty much 24/7 and I needed to train her while I was doing all those things: doing taxes, working with a looming deadline, talking on the phone with clients, making dinner, etc. Trying to be consistent in that environment with multiple priorities is considerably more difficult.