ASOIAF :Why didn't Rhaegar just yield to Robert on the Trident

Why would Rhaegar yield to a man who

1. hated him with a passion that verged on the unholy.
2. Who wanted all Targaryens dead.
3. Who had plunged the realm into a savage civil war.
4. Who had openly defied the king and 300 years of Targaryen rule.
5. was not losing the war; but also wasn't winning it either.
6. had the smaller army

Rhaegar had a duty to defend his life, his childrens lives, the dynasty he was party of, the realm and any unborn son that might have been growing in Lyanna's womb.