Dancers in the long lines do get to interact with more people, but each contact is short and superficial. Squares and short contra sets allow dancers, even newcomers, more time dancing with a more intimate group. Due to their shorter length, time-wise, everyone has more chances during an evening to get into dance sets and this reduces the frantic fear of getting stuck on the sidelines for 30 minutes during a long dance. Maybe there is a reason why, traditionally, contra sets included only six to eight couples. With the experienced dancers split into many smaller sets, a phenomenon like Center Set Syndrome does not occur.
Many dancers approach dancing from an academic point of view rather than the heart.
This is not surprising since many are college educated, but it restricts them, and they get more concerned with the intellectual challenge of the dances than just the uninhibited joy of dancing. They dance to the called figures, but not to the feel and the beat of the music. They become uncomfortable if they aren't kept moving at all times and they have a fear of being inactive. In traditional, visiting-couple squares, as well as traditional contras, dancers spend part of their time being inactive, waiting for their turn to do the figures. Fear of being inactive may just be another aspect of the fast pace of the modern world, or as I have suggested, it may come from a too-intellectual approach to dancing.