The heter mechira came about in the first shmitta year, 5649 (1888), after thousands of years in exile. Some opposing poskim changed their positions when they saw how urgent the situation was. Anti-Zionism caused more opposition.
A young engaged man and his fiancée naturally have very strong feelings for each other. It goes without saying that these will be expressed after the wedding, but what expression, if any, is permitted in the meantime? And while we're on the subject, is the attraction of men and women to each other really a good thing to begin with?