When the loader, excavator or truck leaves the drawing board it's life expectancy was designed into it. Cummins, Cat or Detroit doesn't want to keep building replacement parts for old engines.
They want you to buy a new one. Therefor after so many years it's automatically an obsolete part, engine or piece of equipment. There's no money in manufacturing old obsolete equipment.
And those companies like the EPA rules, emission systems are money makers.