These often occur when one party comes into online dating in a dishonest or uncertain way.
The person may not have a whole lot of social skills nor confidence as a person in the real world and they bring these shortcomings into online dating.
Hence, there have been crazy online dating experiences where a person may show up on a date but not look like what they represented in their online dating profile.
You have to understand that online dating is not a ticket to getting as many dates as you want regardless of how you come across to these potential dates.
Understand that these messages that you are getting no replies to in online dating are going to live human beings.