Fossify Gallery on the official F-Droid repo
The removal isn’t directly related to the buyout/fork. Simple Gallery was taken off of F-Droid due to a dependency on the nonfree Google VR being discovered by IzzySoft¹ ². Fossify’s fork has removed the dependent features to be compliant³.
Aren’t there outside contributors? How can they relicense it without their permission?
they don’t care and as long as no court ruled, they do what they want, which will probably work out for them