Most writers know that the market does shift.
And, because everyone writes at a different pace, a manuscript created today may not have a market by the time it is completed. Five years from now, however, that same manuscript may be just what the editors are looking for. During the 70's, historical romances with alpha-heroes, and heroines in distress, were popular. Contemporary romances as well as historical, featured macho men who occasionally caused their women to cry, but always protected them from danger. In the 80's, heroines became stronger, more assertive.