Luck is basically saying that there isn't any amount of money in the world that's worth sacrificing his mental and physical health for long-term. It sucks for the franchise he plays for who invested so heavily in his future and are now left scrambling to save their season, but you have to respect Luck's choice to walk away from a ton of money to live a high quality of life the rest of his days.
The tweet isn't a bad look for BYU. Brady is passionate about football and about loyalty to team. There are genuinely some NFLers who are so competitive that they would sacrifice everything for the sport and for their teammates. It's a mentality that makes up many champions. It's about priorities and dedication and it's probably more common among linebackers to want to keep going until you can't play anymore.