The key insight is the books are trying to balance winners/losers to maximize their profit, that’s why the line moves. In two-way markets (e.g. a tennis match)

The key insight is the books are trying to balance winners/losers to maximize their profit, that’s why the line moves. In two-way markets (e.g. a tennis match) maybe. With more outcomes, it's a rare market that ends up with the bookmakers locking in a profit regardless of the outcome. For horse racing, the favourite in the race is most often a loser in the book for the betting firm. Even for football (soccer) betting, i.e. team A/draw/team B, generally a bookie is very happy for a draw, because people just can't get very enthusiastic about betting on a tied result. Raising the odds on offer for a draw won't attract many extra regular punters, it only risks luring professionals who are more sensitive to the odds - and they aren't the customers you really want!