You mean having (s) in the end does not make any sense? or that (s) reduces the price of domain by ( 42,300 - 15 = $42,285 )
I would agree what you are saying only if there is only one sports Betting company in the world . But there is probably great competition in Betting business and I have seen many website already working greatly with the same keyword "SportsBettings" with different extensions.
Most of the time Big Buyers Miss out Small things.