I feel that as well. I'm at the point where I am knee deep in my PhD work, and I see that my commitment to that work makes me want to remove myself from other stuff. I just don't want to use any of my energy on anything else, and especially dealing with people in anything but an uncomplicated manner is the last thing I want to do. I am sure it must be doubly so if there is an audience to whatever you say and end up regret.

I have often envied how (I romanticize) it was before social media and hyper-connectivity, where you might be able to just fade out a little bit to focus on a project. Its a bit hard to get that long term focus when people expect you to be available and able to reply within the hour. Just saying "no" drains enough as it is. I don't have the backbone to put out that message though.