He was headed for a potential all pro laden career, and that injury robbed him of it. He had a single season that was decent and otherwise sucked completely for the Cowboys and bowed out of the league unceremoniously.
Probably cost him $50+ million in salary and many years of a career. Only reason it wasn't far worse is because Jerry Jones is a top 5 dumbass in all of sports.
Now that's a worst case scenario and unlikely to happen, but again, intelligent people think in terms of calculated risk.
I know many of the old school fans here like to think in terms of the days when players made jack shit and went to sell houses in the off-season. They'd play for the hell of it because they weren't really risking anything even if the game was meaningless. That was the terrible bowl era that existed for far far too long.
This new era actually gives more than 1 or 2 meaningful games in December/January. Is still not great because of the unbalanced conferences and weight placed on record and not quality of opponents, but it's slowly getting there. At least now the people getting screwed have 2 or 3 losses and not 0 or 1. The sport has moved past the need for meaningless bowl games. The $$$ on the table has blown past the level where playing for meaningless games makes any sense for players going to the draft, or even your starting QB who is returning next year. Why risk Arch, who has taken a beating this season, behind a line that will be missing starters who are leaving for the draft?
If your job told you if you took the rest of the year off you'd get several million dollars next summer, but if you worked the rest of the year (at no pay) there's even a 1 percent chance you wouldn't get the money, none of you would choose to work.
You're expecting these players to think with your stupid fan brain. And unfortunately that pressure causes some of them to make bad decisions. That's why the coaches need to protect them and do what is right for them. And right for the team. This game is meaningless.