Constant changes of direction keep your heart rate high even between scoring plays.
A basketball game is rarely steady-state — you sprint, jump, cut, and stop, then briefly jog before the next burst. That stop-start pattern raises the average effort above what a single sprint or jog alone would produce, since your heart rate never fully settles between plays.
At 6.5 MET, casual full-court basketball sits above jogging but below the most intense gym sessions, largely because full-effort sprints make up only part of the total playing time.