I love this question.
For every registration, sale, guest post contribution, someone stepping forward to lead a group, sharing ideas, there will be many who were close but didn’t get over the line.
These people are almost impossible to identify.
A great question to ask (and you can set this up as an autoresponder) is “what is the one thing that nearly stopped you doing {x}?”
If you’re trying to find out why most people didn’t, ask the few that did why they nearly didn’t.