In the Northeast, contra dance and music have grown and changed together over time. Among contra musicians there's a strong tradition of playing for the dancers, tailoring the music to the specific dance and the specific dancers in front of you. As contra dance spread out of New England through the South and Midwest, organizers looked for musicians and in many places found people playing old-time music. This is also dance music but it's music for old-time square dance, which puts more limited demands on the musicians. Because old-time music was less constrained by its associated dance form it developed a different culture, one in which the dancers were much less central. The standard old-time approach to playing a dance is to focus on playing good music, playing the tune as it should be played, and not pay much attention to the dancers.

With this in mind, it's not surprising that lots of contra dancers will say they don't like dancing to old time music. It's not a form of music that is naturally a close fit to contra and it's not usually played in a way that makes that fit any better.

(The historical component of this post is somewhere between fact, folk history, and conjecture.)