You kinda just answered your own question.
Like a normal person, I have other interest. If i've watched football all day on Sunday, I can take an hour to watch Boardwalk Empire with my GF, or take her out to dinner or something and skip some, all, or most of the SNF game.
If my GF is off from work on a Monday or Thursday, chances are we're doing something together and i'm not blowing her off for Titans/Jags. Sorry. If she's working, and i'm otherwise free, sure, i'll watch a midweek game.
And I don't even have kids taking up my time. And I have a (for the most part) work at home job.
My NFL viewing goes like this. I'm watching all day Sunday. End of story. I'm watching the Rams with undivided attention. End of story. I'm watching Monday/Thursday/SNF if there is nothing else going on in my life. Those games are not 'clear the schedule' games. If it's early in the season, i'm not watching Bears/Vikings instead of a Reds game on a Monday or Thursday. No chance. I'm a die hard Reds fan, the Bears can get lost, i'll channel flip. I probably end up watching 30-40% of the primetime games in full, the rest are bits and pieces or maybe a half.
You can more than competently follow the NFL watching on Sundays. Sports like baseball, NBA, NHL, these are daily marathons, if you are a die hard you need to be into it several days per week to have a feel for it.