Pet Peeve alert: Bad email etiquette

I don't understand how a person does not respond to a direct email. I have actually emailed people for specific information for a volunteer project and received absolutely no response. WTF? Maybe I check my email too frequently, but I always respond to an email. Most people are emailing me to either tell me something or ask me something. How can you NOT respond? I am so irritated by this bad etiquette that I'm probably not going to volunteer my time on this project any longer. And, what's worse, now I don't even like these people because I'm so irritated by their bad etiquette. To me, it's simply disrespectful.