The NFL Network doesn't like how this package is working out for them. It has been a disaster and they need to tweak it or flat out get rid of it or else its only going to get worse.
I'm having trouble finding a source for your claim that Thursday Night Football is a failure and that NFLN doesn't like how it's working out.
The Chiefs-Eagles game last week had the highest ratings of any NFLN game ever (
source).
Last season was the fourth consecutive year of improved ratings for Thursday Night Football (same source).
Thursday Night Football is consistently the highest rated show on cable that day (50% more viewers than #2 last week) (same source).
NFL boosts NFLN carriage fees 41% thanks to more TNF (
source).
Affiliate revenue expected to increase 56% thanks in part to a 10% increase in subscribers.
NFLN ad revenue doubled in 2012 (same source).
I was only able to find a few grumblings (or references to such) and the sources quoted were often anonymous and the journalism speculative at best, often downright questionable (citing ratings problems when comparing to non-cable offerings, for example).
I don't doubt that at least some players and coaches dislike having their routine disrupted and risk short weeks, but NFLN is an increasingly huge cash cow for the NFL and, as Hoodie mentioned above, it is the only compelling reason for NFLN's existence.