The thing about Tesla is that in his early years, he was a brilliant inventor, but in his later years he was quite a crackpot.
Quite true. Yet his fans just say he was getting more and more brilliant. Consequently fewer people around him could match his intellect and insight. So they inappropriately dismissed his later theories as "crackpot" ideas when it fact they were far ahead of the times. There's a self-fulfilling justification among the fans, few of whom are equipped to evaluate his claims technically: they don't have to
understand them; they only have to
appreciate them.
Tesla died in 1943, in the middle of WWII, and the government did seize his papers.
And that's reasonably suspicious to his fans on its face. Not everyone who died during wartime had his papers seized by the government. What made Tesla so special?
I think the answer is simply that wartime makes governments do farfetched things. Consider all the crackpot ideas that were formulated and considered -- incendiary pigeons, etc. On the odd chance Tesla might have had notes on a viable breakthrough, better to have it than not, and better us than the enemy.
It's unlikely that they found, or concealed, anything useful.
I agree. But then Tesla fans happily employ circular reasoning. "It was all crackpot stuff," is what they'd expect as a cover story. If you approach the question with the mindset of the worst Tesla fans (many of which are free-energy nuts), you see a clear motive for the Establishment to hide Tesla's work, much of it having to do with energy supply and distribution.
The crackpot characterization works in circles here too. Free-energy nuts and pseudo-scientists consider first the apparent
novelty of an idea. Mainstream science, they believ, is always just more of the same; no innovation or singular breakthroughs. Therefore if Tesla's ideas seem radical, this helps that sort of person believe they might be the breakthroughs we need, the kind of advances Tesla made early on, and the kind of idea the Establishment would want to suppress.