I think one of the innovations that MTH did was lower the price of non scale engines and rolling stock. My first purchase in over 30 years was a Rail King GG1 at the Big E show in Mass and after that a Rail King Genesis set. But I think the big game changer, for a very short time, was when K-Line started to introduce incredibly low cost scale engines with command control just before their demise. I believe that it was price and scale which changed everything.
Marty