Why Is It?

Wayyyyy back in the 80's, 90s especially I had the machine shop go thru many a motor, 99% big blocks. Usually a 30 overbore, you know the usual, new cam/lifters, all bearings, rings, everything. So a new engine. Most of these ran when pulled, some did not. 95% went went (the existing) with the points dist. New or rebujilt carb and new coil. And back then a repop engine harness was easy to order and cheap enough. (NOT thru Year! though). 95% of the time if I had an issue it was the only OLD part I tried too use, that was the darn old distributor! They all just "looked" to work OK. Never bothered to do anything otherwise. Good and new Mopar parts were easy and cheap enough back then.
Now days, a" new" or rebuilt dist. is a crab shoot.
I never have used MSD but I watch the RoadKill guys hit the highway with at least 3 spare MSD everything!!