Because low kick is better in every way, and is a hg tutor, and bb is a tm :D
Check this out
BB against TTar- 75 bp
LK against TTar- 120 bp
BB against heatran- 75 bp
LK against heatran - 100 bp
BB against snorlax- 75 bp
LK against snorlax- 120 bp
BB against blissey- 75 bp
LK against blissey- 100 bp