I think one of the most common reason is because majority of people are ill-equipped to navigate through Steemit.
We are led to believe that it is so easy to start earning money here and that we become famous.
Such unrealistic expectations of course would result in disappointment and often people would leave complaining about the system.
Even if you have all the best intentions and provide guides, mentorship and a community behind someone there is still a chance that they leave because we really can't make people stay because it is their choice.
We can only offer them an environment that would hopefully make the stay.
"We are led to believe that it is so easy to start earning money here and that we become famous."
who is leading who to believe this? or is it a case the people see the trending page before they sign up and convince them selves they will start earning money and become famous.
I do agree thou, the expectation gap is a problem