I'll try to simplify: you can't readily adjust the tuning of a bagpipe; it's tuned in a way that would make it sound horribly dissonant against other instruments (for important music-theory reasons); and it doesn't even play all the notes, so you can't play in all the major and minor keys of Western (== European from c. 1580 onward + American) music tradition - you're stuck with scales that only make sense for the genre of music that's specifically written for the instrument.