Fewer passengers is its own pleasure.
Smaller ships can have a cozier feel.
Specific ship allocation of public space is a big determinant in whether venues felt crowded. On the Windstar ships, we found the main dining rooms to have comfortable spacing between tables, but even with smaller capacity than larger ships the main dining room volume could get pretty loud at peak times. In the buffet areas there seemed to be less space between tables, so even at less busy times it had a more crowded feel.