Talking from the other side, it’s far harder than you think. Children can be incessant. They seem to be energy vampires. They suck the energy out of their parents, then funnel it right back, in the form of questions, chatter or desire for amusement. Maintaining the correct mindset is absolutely exhausting.
One of the hardest things is balancing being a “parent” with being “you”. If you try and just be a parent, you will burn out, and be a REALLY shitty parent. You need the balance between the two.
I don’t begrudge parents grabbing a few minutes of “me” time, when they can. Unfortunately, some don’t (or can’t) properly plan it into their lives. They then burn out and just grab whatever they can. This leads to the sort of behaviour you mentioned.