They need all the votes they can get, and it doesn't help their campaigns if Americans skip out of voting because they've been told the presidential race is over. National polling hours may help. Closing all the polls at the same time might negate the negative impact of network exit polls. Such an effort would require unusual cooperation by all states, and would be difficult to implement, given the time difference between Washington, D.C., and Honolulu. The best answer is for Americans not to rely on others to do their voting for them.
Voting is more than winning and losing.
It's the one act that sets this country apart from many others. We have peaceful transitions of power. We determine important issues, such as building new schools, in an orderly, fair manner. When we step behind the curtain, it shouldn't matter what the networks have declared, what editorial writers encourage, or what the candidates promise. We have the final say.