I know this is falseflag troll thread but i'll give you legit answer.
1. Didn't need it
2. If you read house show reports from 2003, Nash won title most nights when he wrestled HHH and fans would go crazy but they would do dusty finish.
3. Too injury prone. WWE didn't trust him.
4. He still had heat from WCW days and they'd never push him all the way. Look at how they used every other WCW talent DDP, Steiner, Goldberg, Booker T etc.
5. Nash wasn't bothered. He'd already reached peak of industry many times. He was booked to beat Test on Raw but he had finish changed to Test beating him bc he thought it was Test's time and he'd had his run.
6. He needed neck surgery and got Movie role in Punisher. His contract expired after he didn movie role. They offered him spot on creative but he turned it down.