Let me explain this to you in a way even a child could understand.
Group A: There is a pie. There are 54 people who want to eat it.
Group B: There is another pie. There are 13 people who want to eat it.
Who is going to get more pie on average? Huh? Any guesses?
Is it fair? Maybe not, but maybe those people from Group A should of joined Group B. They probably didn't join group B because there is only a 2 round draft and 15 (most of whom only usually use 13) roster spots among 30 teams compared to the 7 round draft, 54 roster 32 team group A.
That equates to a total of 450 NBA players (if each team uses its 15 man roster). 1728 players on the NFL side.
If the "pie" that you are talking about is the BRI, then you are basically supporting the notion that the NBA BRI should be less--if anything--than the NFL BRI, because there's nothing that says that the BRI should necessarily a given number; it's what they negotiate. In the case of the NBA, the alternative for players is to go overseas at 1/3 the price or start their own failed league, so the alternative to taking their NBA pie and being grateful is to choose a far less attractive pie. The owners don't get any NBA pie until the players agree to a share of the pie, but the owners have other pies; most players don't (unless you count serving apple pies at McDonald's).
You haven't convinced me that the talent in the NBA is more scarce than the talent in the NFL.
Height scarce? Fine. Use players a bit shorter. And they did.
Shooting scarce? Not so much anymore. Ronnie Brewers aside, more players are coming in as good shooters.
Athleticism scarce? The NBA is far more athletic than it was, say, 20 years ago.
Defense scarce? Well, that's another story.
The fact that there are more players on an NFL team is not particularly relevant, given that there are 10 or 20 football players and basketball players who graduate or leave school every year per available position; i.e., the possible labor supply is far higher than the demand. Not every college athlete is pro-worthy, but that applies to basketball and football.
Each year, the NBA labor demand is probably somewhere between 30 and 45 players. The NBA doesn't have much turnover; because NBA players are p-u-s-s-i-e-s compared to the NFL and usually have longer careers. I estimate that about 4000 upperclass football players are eligible to declare for (7*32 =) 224 NFL spots (plus free agency). Of the 300+ basketball teams, a minimum of 3 or 4 graduate or leave school per year, leaving about 1000 players for (generously) 60 spots. In both cases the ratio, is somewhere between 10 and 20 to 1. Nothing in this ratio suggest that basketball players should command the vastly higher salaries than football players.
In other words, the NBA players should take 50% (or maybe 51%) of the pie and be extremely grateful, given that they are not all that scarce and get more pie per person than any other pro league.