Why do larger companies sell off?

I have noticed a couple of companies pop up now and again selling complete truck mount vans, when a certain number of hours are hit on the machines.

Maybe it is tied to mileage?

I wanted to know if at x amount of hours maintained or not you can bank on the truck mount costing you more to service than it is to build a new rig?

I'm not an expert on truckmounts and their inner workings, so I will look at this through  a financial & business spectrum. 300,000km motor is no worst that a 150,000km motor if properly maintained, if compression is good & many parts have been changed ( rad, valve job, heads, wires & plugs, hoses and belts ) then grab it and if you get it cheap, then you're ahead of the game. All of my equipment is old and working fine, I mostly do large commercial accounts where I leave my equipment there on location such as polishers, burnishers, portables, or a truckmount ) I have 2 old truckmounts on location not even plated cause they never left the location for the past 4 years and these are the old driveshaft cleanco models. They sit outside through the harsh Quebec winters, and start up every spring like a charm. Don't be afraid to buy a good old used unit, you'll get your money back plus a hefty profit, providing you have the work.

A deal is a deal, I know it when i see it.