成唯識論演祕 4.279

4.279

但簡行蘊心所法故。又行蘊命亦是主故，故言少分，此文不次，結前第三所簡法故。

Because it only eliminates the mental factors (caitasika) of the saṃskāra aggregate. Furthermore, life-faculty (jīvitendriya) in the saṃskāra aggregate is also a principal [factor], hence it says 'a minor part'. This text is out of sequence, because it concludes what was eliminated in the third [section] above.