And TOS has not? This fact didn't stop CBS from updating it.
TOS was at greatest risk of vanishing from the "want lists" of syndicators, as they anticipate the arrival of HD TV.
Also, the remastering of SPFX has gotten more people talking about TOS, debating its merits and inadequacies, and we now have formerly-resistant TNG-era ST fans sampling TOS for the first time. Word of mouth will help bring about curiosity for TOS as we build towards the release of the JJ Abrams' TOS-era film. It's all part of ongoing product recognition.
There's no rush for remastering TNG... yet.