This is a general question for all of you who build Saas as a business. Do you find the problems to why people don't use you product after sign in? If yes tell us about it :) !
big topic! are you asking for yourself or looking for other peoples' perspectives?
The best answer is the visitor did not find enough value. And be cautious. You can get the wrong match of visitor and your solution. This is pretty common. Not every user is best suited for your solution.
Ok that is simple.