Video report from Al Jazeera:
The report makes it clear that Hamas' reasons have nothing to do with any tree disease and everything to do with inconveniencing Jews.
By the way, if they are really losing $1 million and they planned to export 100-200,000 lulavim, that is quite a profit they would have been making! My understanding is that the usual wholesale price to farmers is closer to $3 each than $5-$10.
(h/t Allen L)