Back of the envelope, every viewer of MNF would need to pay $200 just to keep MNF and one wildcard game. More to get Sunday, Thursday, the playoffs and the Superbowl. Easily $300 - $400 per viewer a year.
That's a hard sell.
Can't watch ALL games live right? That's hardly completely superior. IMO, NFL would make less money on direct sales than they do when they charge networks which charge all cable subscribers (even via retransmission fees for those of us who can't get OTA) AND charge advertisers. That double dip is going to net more money than a specialized service for NFL fans.
You can't on television, either.
I pay about $30 to Sling TV just for Redzone. I've never watched any of the other channels that come with it. When the regular season ends I just cancel Sling.
I'd be happy handing over the $150/season or so directly to the NFL. Unfortunately, I'm probably worth more to advertisers just because of that.