Final answer:
The DJ's purpose was to see which songs make people dance.
Step-by-step explanation:
The purpose of the DJ's action was to see which songs make people dance.
Dance is a recreational activity, and one of its purposes is entertainment. DJs play different songs to see how people react and which songs get the most people dancing. By observing the number of people on the dancefloor during each song, the DJ can determine which ones are the most successful in making people dance.
Reference: BBC Earth - Where did the ability to dance come from?