While I like a good conspiracy, it seems to me as though this was a perfectly appropriate outcome of technological advancement. Surely old storms would be biased high given a variety of reasons.
No conspiracy needed. After all, the first time a hurricane was intentionally flown into by a storm was only in 1943: https://en.wikipedia.org/wiki/1943_Surprise_Hurricane. The 1950s and 1960s are not that far removed from that initial attempt.