Ok, I have a question (actually after writing this I have a few questions

),
Why do some people initiate contact..send an email to you telling you they're interested..and then not follow up after you respond?
You reply with an email saying 'I'm interested, here's my email' and then, lone and behold, nothing?
Other than the obvious..maybe they have found someone else they're more interested in...but it's happened to me a few times and I'm wondering why?
Does anyone have any thoughts about how long you should wait to respond? And why people do this, it's driving me nuts!