In addition to the good reasons for doubting this explanation of 1975 already given. I would add that there is simply no evidence that JWs' status as a proselytising community has ever been in doubt. Especially in the United States where they fought many legal battles on that basis. They may have preached more leading up to 1975, but they were also highly active preaching before the prediction, as well as following the failed date.
And as others pointed out, the evidence is that Fred Franz was the driving force behind 1975. If there is any evidence he was motivated by legal and financial pressures, rather than what he appeared to be, caught up in his own obscure biblical formulations, it's not been presented.
Plus 1975 was not first mentioned in 1966, as another poster careful has pointed out, this date was indicated as early as the 1940s.