That's a good point. But I think we're talking about two very different composers. Philip Glass is a committed minimalist. The leitmotifs in his music originate from minimalism and feed back the minimalist ideology. Morricone, on the other hand, may be influenced by certain aspects of this style, but he is not a minimalist. Besides, leitmotifs are not unique to minimalism.

So it can be said that the main difference between Philip Glass and Ennio Morricone is about being a minimalist or not. Hence, the function of leitmotifs is different in each composer. Nevertheless, this is a good discussion. Maybe it's also worth writing on Philip Glass as a film music composer. Thanks for the comment.