That's because, since their inception, nobody has been able to come up with a model that rival candidates would accept, and that would be useful and informative for the viewing public. The only debate arrangement everyone agreed to nearly 60 years ago largely remains in place today – the game show format.
The first TV debates were shaped by federal regulations, an enterprising network executive named Frank Stanton, and a series of negotiations that were hampered by a tight schedule and dueling campaigns.
News. Community. Debate. Levers for better democracy.