Just wondering why there is only one TNG book being released (LTP) over the next 18 month period, in comparison to all the other series.
Why not?
Yes, in 2007, we got a bunch of books in a short time frame, primarily as part of the celebration of TNG's 20th Anniversary year. Since then, though, the schedule has been about what it is now -- one TNG-labelled book a year, give or take the odd multiseries trilogy here and there.
And, as said above, the 2010 schedule is still very nebulous, though it can all but be guaranteed at least one of the "Typhon Pact" novels will be a TNG book.