It's because they just can't afford to devote what used to be the somewhat inconsequential cost of cast iron and spend the time and money in building a quality machine, one designed to last generations. I'm certain current machine manufacturers would beg to differ, but there's not much denying that along with the advancements made in technology (read: electronics), coupled with the never ending pressure of competitive pricing (read: relative inexpensive Asia labor), they can no longer 'build 'em like they used to.'
During the build up of the industrial revolution, industrial machinery manufacturers would 'sell' the fact that their machines were built to last and in case of failure, were easy to get up and running again quickly and cheaply. It may have been one factor in their eventual demise in that in the wind-down of the industrial revolution, there were not enough new factories starting up to feed the need for all of these great machines and with the ones already out there, ones that would last forever, a now obsolete customer base.
I'm not sure how it is now, but a few years ago when I was buying our machines and setting up our shop, these things were going for 'a song.' The world economic collapse was fresh and the furniture manufacturers in the midwest and east coast were 'dropping like flies.' They were either closing up for good or moving their manufacturing to China, but in either case, they were not keeping or taking their machines with them. This one (a classic Northfield 4) came out of the Riverside Furniture Corporation factory in Russellville, Arkansas. Riverside, along with hundreds of others closing down, created such a glut of old 'arn on the market, that these things were going for practically nothing, This one's purchase price, rigging and freight to the west coast, cost less than the new Amana blade and replacement power feed rollers cost me once I got it here. It was really sad to see our great furniture manufacturing base decimated as it was but it has been only one of many industries that suffered the same fate. Perhaps it is with their demise and the spawning of the Walmart / Ikea concept that will give opportunity to guys like me, custom guys, but only time will tell on that one. As it is right now, it's pretty tough being a 'custom guy.' People may like 'custom stuff' or the idea of it, but they also like the Walmart / Ikea price and there seems just too little appreciation for quality anymore.