People who are super busy don't have the time to spend minutes first reading, then processing (and/or rereading), then responding to your email. This is simply life, there is only so much time in a day, and some people have way more constraints on their time.
Spending lots of time parsing/processing/understanding/formulating responses/replying to emails from people they don't know or have reason to care about? Probably not high on their list of priorities - which for the record is probably already completely overloaded anyways.
Write shorter emails (or electronic content) which are easy to answer. This ability is an art, get used to practicing it if you want responses.
Make it easy for someone to respond.
Practical advice from this question
Notice that even in this question, the important part
Why is this acceptable?
was buried in a large paragraph (assuming this is even your primary question, which I'm assuming it was). Plus, it was filled with irrelevant information which suggests other things are what you are interested in.
If I'm a really busy person getting hundreds of emails a day, you just made me read, then reread the email after finishing to figure out what you want a response to. You can't do this if you want responses consistently - and this is relatively SIMPLE with minimal text.
I just find it tremendously frustrating when my emails are ignored by
faculty (both at my institution and at other places) and I don't hear
back at all. I understand that I'm not really in a position to
request anything of anyone, but it just seems like common decency to respond rather than say nothing at all
- Why is this behavior acceptable?
This is considerably more clear and makes it easier to respond to.
If you are not naturally able to write clear, concise, and easy to respond to emails, practice and spend time rewriting them until you feel they are.