What's the deal with some of these NFL players?

Because the NFL contracts aren't fully guaranteed unlike the MLB and the NBA. While some contract renegotiations are because the player wants more money, most renegotiations are due to players wanting more money guaranteed for a longer time. For example, say a player signs a 5 year 50 million contract where 20 million is guaranteed and he receives an equal $10 million a season. At the end of the second season, the team could cut the player or the player could suffer a career ending injury and the team would just get rid of the player and not owe the now ex-player a dime!

As for the top players wanting to be paid the most, honestly, I have no problem with players leading the league and getting paid for it or wanting to be paid for it.

Think about it if you were in their shoes. If you were making a ton of money, but you knew you could easily be making a ton more money somewhere else. Or if you play your heart out for a team and you are still basically their best player and they say we are going to cut your passes down to less than half like the Texans stated to Johnson when he was still averaging over 1,000 yards a season and in his last Texans game had like 173 yards.

Or if you are playing twice as well as someone else and they make more than you. It's easy to say they should be super happy with all that money not being in their shoes and not making their kind of money. However, they have to take another thing into factor. Major injuries. How good will their health be by the time they retire. Many of them can barely walk several years after they retire. Look at Joe Namath's health.

Their agents also push them to get more. The more the player gets the more the agent gets. Even if the player doesn't really care as much about the money, their agent will talk them into wanting more

They're human. Most people want more money then what they're currently earning. It doesn't matter if they're making minimum wage or $80,000 a year or $12 million a year, they want more.