Why aren't the runners coupled?

loads of reasons. first is that most people would prefer to pick the winner and sometimes you get one part of the entry with no hope, so why reduce your potential winnings with a coupling? Also you often get one half of the entry withdrawn/scratched and if they were coupled on BF then that would cause a massive headache. But lets face it coupling is pain full stop.

The tote has a profit margin of 23%.If you back a coupled horse on there effectively you are dutching your already perceived loss by multiplying their advantage by your stake.