William Shatner's novels did try to be consistent with the Novelverse. Captain's Glory had Miranda Kadohata, Aili Lavena Xin Ra-Havreii and Christine Vale in it. In every instance where the Shatnerverse is inconsistent with the Novelverse such as the year of Bajor's admission to the Federation, it was a Novelverse book (Unity 2003) contradicting a previously published Shatnerverse book (Captain's Peril 2002). So the Shatnerverse wanted to be part of the Novelverse, but the Novelverse kept saying "no, get away from me".
That's not quite true. Yes, that one book did borrow
Titan characters, but it used them in a way that contradicted the
storyline of the three previously published TTN novels. In those novels,
Titan helped out at Romulus in December '79 (
Taking Wing), got whooshed to the Small Magellanic Cloud for most of January '80 (
The Red King), and had started its primary mission of exploring uncharted space by March '80 (
Orion's Hounds), at which point it promptly made first contacts with a number of new species. But in
Captain's Glory (published 7 months after
Orion's Hounds),
Titan stayed at Romulus for pretty much the whole of 2380 and didn't make its inaugural first contact until halfway through 2381 (around the time
Over a Torrent Sea happens in the TTN novels).
Borrowing characters from another work of fiction is not synonymous with sharing its continuity, since fictional characters are just ideas and can be plugged into any continuity (see Jimmy Olsen, Harley Quinn, X-23, Phil Coulson, Grand Admiral Thrawn, etc. -- or for that matter, see all the contradictory Trek tie-ins that use the same canon characters). And none of the earlier Shatner books borrowed from the other novels. The use of
Titan characters wasn't the Shatnerverse trying to be "part of the Novelverse," it was the Shatnerverse borrowing elements from the novels that it found useful for itself, and reinterpreting them in its own way. The Shatner/Reeves-Stevens novels were written for a different audience than the main paperback novel line -- a more mainstream audience looking for hardcover blockbusters by celebrity authors -- and since the two lines were not going to be read by all the same people, it was decided that it was best to let them strike their own independent courses and not be restrained by each other's choices.
Recall that some years back, there was a
Star Trek exhibit of some kind that used the
Titan design created for the novels and made a short film with Tim Russ, borrowing the novels' concept that Tuvok had joined
Titan's crew -- yet it also contradicted the novels by putting Wesley Crusher on
Titan as well. The reason these different things borrowed characters, designs, etc. from the
Titan novels wasn't because they wanted to be in the novel continuity, but just because that was the only established version of the
Titan so it was convenient to draw on its ideas.