The variety of triads in minor scales is greater because there are three types of minor scales: natural, harmonic, and melodic.
Triads in the natural minor scale:
M = major; m = minor; d = diminished
Triads in the harmonic minor scale:
M = major; m = minor; d = diminished; A = augmented
Triads in the melodic minor scale:
M = major; m = minor; d = diminished; A = augmented
See C > Chord for related entries.