There are lots and lots of reasons.. I'll give ya just ONE!

A guy's Jeep is running badly. (all he needs is new spark plugs) He has no idea what is wrong with his Jeep. So he gets on a site and reads posts like yours..
So he does the whole enchalada.. plugs, wires, TFI..everything he has read in Marty's post..

His ride now runs like it did when new! He is a believer! So HE starts posting..How wonderful the TFI is and what all it did for his ride..Milage! Power! Smooth idle! Hell it even SOUNDS better!

The guy never knows all he had to do was spend the $20. and install new plugs..

That's how it happens.

Hey I (we) have no problem with tinkering with your engine. If a guy has fun installing a TFI or any other modification to his ride..I'm Ok with that.. As long as he KNOWS it won't do one damn thing.. other than LOOK different.
Big JIm