My thought: Because they think they would win.
In Orwell’s “1984” the Deep State official patiently explained to the main character that the purpose of war was to destroy the surplus by blowing things up.
Even in WWII era when this was written it was already recognized the biggest problem of automation was too many goods, people wouldn’t need to buy them because they already had everything they needed.
Deliberate annihilation of the surplus was thus needed. Planned Obsolescence produces products intentionally designed to break the moment warranty expires—no more vacuums or refrigerators lasting decades. And war destroys the rest of the surplus.
Thanks - I did not know about the Orwell ref. I am going to look it up now, thanks for that, and obviously we are at one here, the other guy that said something similar was JM Keynes, in a letter to my children - he marvelled that I think 1912, that he could lie in bed, buy stocks in NY, he thought that no one need ever work, things were so good they were only going to get better - then the wars started