Unlike baseball, the NFL has a salary cap on player spending that limits what even the richest owners are able to do to improve their team. NFL GMs can manipulate the cap with various accounting gimmicks such as prorated signing bonuses to spend more than the cap amount in any given year, but there are always consequences down the line. It’s worth it if you get a Super Bowl out of it, but if you misjudged the talent you spent the big bucks on, you’ve got a problem.
Ideally you’d like your team to be good at identifying value so that they get the biggest bang for their buck.