according to the link you posted, top 10 gets a share of that $1000. Currently there is only one entry if I am not mistaken.
Yes there is one entry only at the moment, it is because most of the eligible matches are started yesterday on my timezone (4 matches ended already). Perhaps the other potential participants are betting on the other matches that will start today. There are still so many matches to bet for the soccer tournament, I believe there will be more participants till the end of the tournament.