It occurred to me that you can think of the accordion as two different instruments, one with right hand single note and another with right hand chords. Dyads come somewhere in between. As accordions are chorded with three- and four-note right-hand chords, the music can get muddied and songs become more alike. Single note songs do not inherently sound alike on accordion; the range is greater.
It’s as if for North Americans and Western Europeans the chording subconsciously reminds people of polkas—the multi-notes all sound a little or a lot like the accordion’s inner polka trying to get out. And while polka is wonderful, you don’t want your other songs semi-automatically sounding like polkas. It takes extra work and musical ear to make sure that a chorded song does not sound muddy or more like a polka than you wish it did.