Perhaps the engineers don't care that a plant works for a long time, but it certainly concerns an industrialist who buys it to put it in his own company. Anyone wishing to buy the 1MW plant would surely pay it a lot of money, he should adapt his company so that he can exploit it and then have to base his future production on the certainty that that plant supplies the necessary energy with continuity and safety. Would you do this for an object that was only tested for a few days or a few months? Or would you like to make sure that what you are buying will work for at least a year? And this guarantee, who can give it to you, if no one ever did a long-term test on that product? These are basic concepts, don't you really realize it?
SSC - you need here to join the dots. I don't think you can be an engineer. At least not an experienced one.
IH could happily do a long-term test themselves. Indeed, i'm sure they did, and got stable results over time. The problem is that those stable results were positive only on spoofed Rossi/Fulvio tests and COP=1 on genuine independent tests.
The Rossi 1MW test was useless for this purpose since it was not properly documented. Rossi was there tinkering with things, mending non-working reactors, etc, etc the whole time.
For commercial reliability measures you need to document failures, and investigate failure modes. All of which IH could do (and had ample time to do) in-house. None of which was done in the long-term test.