Because the TNG movies have crashed & burned. You could argue that's not the fault of the actors so much as writers/directors, but once something is tainted by the mark of loserdom, Hollywood is unforgiving.
That article dodges the real reason for the prequel: Kirk and Spock are still the most recognizable names in Trek. But that might be less the reason that Abrams, Orci et al decided to go back to TOS than the reason the suits greenlighted their concept and not some of the others that have been kickin' around.
To Orci & Kurtzman, the movie is a chance to pay tribute to something they love but to the suits, it's a way of revitalizing a lucrative brand. If all goes well, both parties should be able to get what they want (and the fans, too, except for the ones who are determined to be unhappy).
I wouldn't be surprised if in the far flung future, TNG (and DS9, VOY & ENT) characters are recast and revived, but I think it's more likely that the success of the TOS recasting will spur spinoff series based in the 23rd for the time being. By then all the series besides TOS will have been long forgotten.
2) TNG was the Trek series that entire families watched together - that's not boosterism, it's a fact reflected in the demographic measurements of the audience (and it was far more true of TNG than of TOS or any of the spinoffs to follow).
I think TV viewing habits have changed too drastically for it to be worth anyone's while to go back to TNG in a forelorn hope of re-capturing the old glory days when there was any such thing as a mass market for shows other than really lowest-common denomenator reality TV and cop shows. Parents and kids simply don't watch TV together anymore and trying to force the issue is silly when there are easier ways to make money than fighting against prevailing trends. Since when does Hollywood
fight trends?
If any of the spinoff series are revived, it will be in the context of modern viewing patterns, in which any sci fi series serves a niche market - which can be perfectly lucrative since the smaller market you get is also more committed and willing to buy DVDs, pay for downloads, etc. It's just a different business model.