Jon,
Glad you enjoyed the lesson. I’ll be doing more of these in the future. Good question.
The main reason I did that was to make the right hand picking pattern easier. To grab all three notes of the triad (thumb, index, middle) after the 8th note rest you’d have to do a quick double-thumb to play the note on beat 4 of measures 18 and 20. You could probably make it work but it wouldn’t sound quite as smooth to my ear. You could try it and see how quickly you’d have to move your thumb to play on the and of beat 3 and on beat 4.
You’ve already played the full triad on beat 2 of those measures as well so that also factored in to my thought process. You’ll probably hear plenty of the chord already and I was really thinking more rhythmically here than harmonically.
If you have any more questions let me know!
-Mike