Assistance Needed

As you hear the news of who played tonight and who didn’t, something struck me that I need some help on. Can anyone explain why the NFL declares players inactive before the game starts and has rules regarding use of the third string QB?  Seriously what genius came up with both of these ideas?  

Was the thought we want to make it tougher on the players and not have them sit until they are close to 100% before ready to get back into the game?  Or maybe let’s have them travel with us but not play?  Then with the rules on using the third QB are you serious.  Could you imagine in baseball if the rule was you can not use your closer before you use your set up man or in basketball if Kobe gets into foul trouble the Lakers couldn't decide to use their 12^th man over their 11^th man.    I can’t help but think Andy Reid would rather get Mike Kafka a little experience if say the score is 35-3 in the fourth instead of Mike Vick.

I don’t know many people who love pro and college football as much as me but these rules make no sense.