I get it, but can you even buy 'simple' these days? Every engine out there is computer controlled nowadays with miles of wiring everywhere. Line up a new Kubota, Deere, Kioti, or Yanmar and the wiring would stretch to the moon and back.
My '52 8N is simple, but it has sat for weeks not working
http://www.tractorbynet.com/forums/parts-repairs/386941-busted-8n.html.
I will say that while modern tech can be overwhelmingly complex, it has a lot of benefits. Modern cars go 100K miles without even needing a tune up. Modern tractors are similar. They will probably out live us. However, I can see the cost of repairs being what sends them to the junk yard.
Even though my old 8N is no where near as productive or reliable as a new one, I can buy an engine rebuild kit for it for $250 and keep it running indefinitely on my own.
Everything is a trade off...