What is it that they are threatened by?
Could it be that the The gif shows a cloud seeding operation at the moment when the seeding apparatus was switched off before another grid pass?
Can you think of another reason why they would delete it?
We will disagree, as the provenance of that clip seems relevant.
How do you know that Imgur.com was “threatened” by the clip? Have you contacted them about that specific clip?
Unknown.
Perhaps some sort of copyright infringement? Or the clip was found to be attempting to deliver a malicious payload? You seem especially curious as to why the clip was deleted. It seems contacting Imgur.com is in order.