A lot of people today barely talk about their income, now for salary earners this may be normal/agreeable to some degree(as most company's policy kicks against it) since salary to some extent tells a lot about the company's work force, weakness and income to 
their competitors.
The big question is why do most self employed individuals even crypto dealers, steemit whales etc try so hard to keep their earnings from from friends, families,sometimes spouse.
A random interaction with a few explains this act is directly linked to the fear of the "unusual sense of entitlement" and the most interesting stuff about this fear is that it is sub-conscious and spontaneous. You just find the strong resistance not to disclose or to even lie about your earnings.
The findings of the research is summarised as thus,
... There is a tendency that when individuals with any form of ties discovers a raise in your income, how much you're worth or have gotten with the bank, the unusual sense of entitlement automatically steps in and even the little they would normally appreciate becomes an insult not minding your personal welfare/responsibilities.
An understanding of this concept will help one realise that this resistance or non disclosure of income is more as a result of this fear and the action is mostly sub-consciously driven