Unity had nothing to do with the closure. Ubisoft has been in a poor financial state for the past few years and in an effort to recuperate, several projects have been axed and internal studios either downsized or shuttered completely. Unfortunately, a majority of the FGOL team was let go as part of the continued corporate downsizing of Ubisoft.
Currently, both Hungry Shark games are now managed by the fine folks at Ubisoft Barcelona Mobile