I don't believe in unpopular sports betting. but for quite a lot of types of sports betting, I can see it in stake and sportsbet. Because I prefer football betting, I don't pay much attention to other sports betting. boxing and MMA may be something I try occasionally but the others are very rare.
However, those who do business in sportsbooks will focus more on bets that have many fans. it will benefit them. but for bets on certain sports that may not be in great demand, they may not be listed until a member may provide suggestions.