So what's the difference of PVE being a job or your description of PVP taking a lot of time and practice to be good. How is it you could lose your wife and kids spending all that time PVE, but not with PVP?
PVE in WoW often referred to as Raiding is like a job. There are set times you play through the week. And while your playing there is not much stopping.
For example, 4 nights a week, 5+ hours a night. During that time I would have to set my attention to playing, consistently. Yeah I might be able to run to the bathroom but all in all, my attention is on that and nothing else.
So how could that cause problems for me at home?
My wife wants help with something, "Honey Im giving Lily a bath, can you change Ophelia?" If everytime she asks me to do something small or large my response is "Sorry Im raiding..." I dont think I need to explain how that would cause problems.
However, if I am just doing random bgs, I stop when I want to stop.
If I was doing arena with a friend, its not a big deal to stop because I am only asking for one person to wait on me. In a raid situation, that would get very old for them too quickly, because I am asking a whole raid to wait on me. And what if lots of people did that, you wouldnt get anything done.
Now if I was single, and no one was waiting on me, awesome. It wouldnt matter to me to burn through some time raiding.
WoW in general can take up a fair amount of time, but at least with what I like to do, WoW and the PvP work around me.
As a direct answer to your question, Pve Raiding is not flexible because of the amount of people it takes to get done. However PvP is often done with a friend or a couple friends and its much more flexible.