That is an Ijma and is for safety, because At the moment, there is no technology available that would allow for a return trip from Mars (source)
In this link you can find:
The committee of in the UAE that issued the fatwa against such a journey doesn't have anything against space exploration, Elon Musk's Mars visions, or anything like that. Rather, the religious leaders argue that making the trip would be tantamount to committing suicide, which all religions tend to frown upon.
Perhaps, when there is enough advancement to make a round trip or if Mars is declared suitable for habitation, the consensus will be lifted.