While the actual observance of Thanksgiving is varied on the Human worlds of the Federation, it is a holiday that is quite popular within Starfleet. Indeed, it is one of the Human holidays that has been embraced by many other species if they do not already have a similar one of their own.
The opportunity to gather together and give thanks for what we have is very much enjoyed by Starfleet crews, especially on the exploration ships which often face dangerous situations. We are all far from our families, for it is rare that our opportunities for shore leave coincide with major holidays, whether they be Earth Human celebrations, Vulcan ones or those of any other species.
Indeed, the Captain has often stated that a starship crew is a family in its own way and there is much in the way of logic in his statement. In light of that opinion, he has always done his best to ensure that the Thanksgiving celebrations on the Enterprise were as inclusive as possible, a difficult prospect when one considers the number of different peoples who serve aboard her.