I'm quite comfortable sharing my ignorance, and perhaps this is no exception.
I'm sure there are many reasons for vintage love, but right near the top for me - simplicity. Holy crap...every time I dig into one of my Vertigos, the 800XC, the Xtrainer or even the fairly basic XT250's - I can count on it being several hours for most anything. I'm slow, but still.
I could tell by looking at this bike it wasn't complicated, but man...under 10 minutes, start to finish to yank a TY engine. Yank carb, exhaust and three bolts. I kinda like that.
Say when, John - I'll be over. Heck, since you're gonna be helping me so much - least I could do is take 30 minutes and yank a couple of your TY engines.