Earlier quoted context omitted.
Sometimes people get busy and overwhelmed, but they don't know how to say no.
I know a lot of people that don't get through their email every week, for example. Even saying no takes too much time, with the volume of communication required by daily work.
In the event that you actually do end up emailing me, it's contingent on me actually checking my personal email, which I never do when I'm not working, and only sometimes do during work hours.
If it's you asking me a favor that I'm not in the mental space for, I'll mark the message unread as a reminder to get to it later.
Maybe I just have weird email habits, but I can get away with this because email is not a heavy part of my job.
That being said, one guy was pitching me on something several times a month for several months. I just recently responded to him and apologized because of x y z. He said don't worry and we had a fruitful conversation later.
So, follow through is important!