It wasnt always in crypto but I've seen alot of parimutuel betting sites and if the site is just trying to accumulate users it 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.   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.