[Farm93]

Can someone explain to me how this rule helps the NFL?

The article notes the NFL explains it is in place to encourage players to stay in school.  The NFL gets a fair amount of mileage out of their youth sports outreach efforts.  The PR associated with stay in school messaging here is probably helpful to those efforts.

Likely the union wanted it too.  A lot of NFL players stay in the league for 2 or 3 years and then suffer financially.  Anything the union can do to get players to get their degrees is likely supported by the former players now in the "I wish I knew" club.  There are a lot more former players than soon to be players, so I would hope former players want this rule.

The rule also helps those that actually want to graduate.  If the league allowed soon to be rookies practice if they are no longer in school, then the teams in the league would almost certainly draft drop outs over those still taking classes.  That would then mean college players, many without a real chance to get into the league, would drop out of school hoping to improve their chances of making a team as a draft pick or getting selected as an UDFA.  In theory, those players could return to school later, but that is tough for many socially, psychologically and financially.

There are others I am sure, but my bet is the league has maintained the rule largely for PR reasons.

The real issue here is that Stanford's calendar year runs late relative to other schools, so CMAC is unable to join even though most of the other rookies are now on the field.  If Stanford finished up in early May, like some other schools then this would not be an issue. 

[Farm93]

Can someone explain to me how this rule helps the NFL?

The article notes the NFL explains it is in place to encourage players to stay in school.  The NFL gets a fair amount of mileage out of their youth sports outreach efforts.  The PR associated with stay in school messaging here is probably helpful to those efforts.

Likely the union wanted it too.  A lot of NFL players stay in the league for 2 or 3 years and then suffer financially.  Anything the union can do to get players to get their degrees is likely supported by the former players now in the "I wish I knew" club.  There are a lot more former players than soon to be players, so I would hope former players want this rule.

The rule also helps those that actually want to graduate.  If the league allowed soon to be rookies practice if they are no longer in school, then the teams in the league would almost certainly draft drop outs over those still taking classes.  That would then mean college players, many without a real chance to get into the league, would drop out of school hoping to improve their chances of making a team as a draft pick or getting selected as an UDFA.  In theory, those players could return to school later, but that is tough for many socially, psychologically and financially.

There are others I am sure, but my bet is the league has maintained the rule largely for PR reasons.

The real issue here is that Stanford's calendar year runs late relative to other schools, so CMAC is unable to join even though most of the other rookies are now on the field.  If Stanford finished up in early May, like some other schools then this would not be an issue.