I can suppose that other famous players are already busy. Or among other players, Suarez is famous for his biting. I dont think that Duelbits are focusing on Brazil only (not because Suarez plays in Brazilian club definitely, because Duelbits are official sponsors of Premier Ligue club), but they are focus on South America in general. Suarez play for Brazil club, he is from Uruguay itself, and Argentina with new president (who cheers for Bitcoin) is near.
I feel like there are two things that you do when you are looking for an ambassador, first of all he needs to be someone that you can afford, which means that there are some players (like for example Ronaldo or Messi as biggest examples) you can't really afford and you just delete them from the list right away, secondly it needs to be someone who is already not working with someone that is close to your business or prevents them to work with you.
When you get rid of these two lists, whoever is left as the best player on the list gets the job, and Suarez could very well be the most famous player who is not unaffordable and who is not really doing anything that would end up with a huge return one way or another, he is available and very famous.