All sports casinos should be parimutuel imo. I also don't understand why there is only freebitco.in uses that idea. Maybe they don't use it because:

1- They are lazy and they don't know how to code it or,
2- They don't do it because it requires active players on the casino beforehand to make it work.

Either way it is a great way to build a casino for both the players and the owner because it is all automated rates and everything. There is no risk for the house to get scammed because of a fixed/cheated game because the house takes its cut no matter who wins. (this has been an excuse to seize the players' money for many casinos)

This is almost as close as you can get to a decentralized sports betting casino.

It wasnt always in crypto especially but I've seen alot of parimutuel betting sites setup and head into esports or similar and if the site is just trying to accumulate users parimutuel can lead to erratic betting odds that can prove unattractive.   There is the problem of size where a very large bettor can move the odds and alter the pay off at the last moment even, it can lead to a feedback effect where people are wary of the odds being such a free float.   I've also benefitted this way, one bet I placed got a 83x pay off because it became lopsided and my underdog came through but overall its something of a problem to handle for sites I think.  
  Freebitco is maybe ok with this as its such a large established site that has regular custom and people will just drift into the event section and place bets but alot of sites are struggling to raise confidence in bettors to participate or even visit.