They are too smart to know those who deposit to test the system to see if it pays or not and those set of users usually stake with a little amount, in cases like this they sometimes payout those smaller amounts to give you self motivation to come back with a high stake and to have some kind of society backup. But their major targets are high stakers. They act like a Ponzi scheme( pay 100 people, scammed 10,000 people )
Of course, you pay $10 to 100 ordinary people and you get a great base of satisfied users who will spread the good news through their social networks, and in addition, they have an additional motive in promoting their ref links. Then a player appears who has made a deposit of say 1 BTC and when he says that his money has been stolen, his voice in the crowd of 100 votes is almost inaudible.
As some others said, Mycelium probably didn't do a proper due diligence.
Maybe, and maybe they don’t care as long as they benefit from promoting such services. I am of the opinion that it is not professional to make such a mistake, because if you provide a very serious service, then you need to be especially careful what you advertise within that service. Any user of this crypto wallet who becomes a victim of this scam bookmaker will surely become a former user.