The novel currently has 359 reviews and it doesn't even have Star Trek on the cover.. Federation: The First 150 Years by the same author has 283 reviews. Most of Pocket Books' novels don't have anywhere near those numbers. Does Titan Books have better marketing than Pocket Books?
Well at least with the Autobiography I guess it certainly helped that Shatner was at least a bit involved with the PR, i.E. he read excerpts at SDCC etc. Add to that that these kind of release are more of an "event" than the steady stream of release from Pocket, so they got more coverage from websites who usually ignore the prose releases.
It's also the kind of book people buy for friends who are hard to buy for, ie. for people might not collect the regular Trek novels, but an autobiography of a famous fictitious character makes a whimsical gift. I don't recall the author canvassing reviews online.
That's what I did. I send a copy to a Trekkie who does not read the regular Pocket line. It is one of those books that is easier for regular people to pick up and read than the ongoing novelverse. It has wider appeal.
The book was also much more widely distributed - I picked my copy up from my local supermarket. It stuck around in stock through Christmas 2015 (the paperback edition also got a release there the following year) and was marketed as more of a 'novelty' product and interesting gift idea.
Just a few days ago it was offered for $1.99 on one of the bargain ebook newsletters, and that might not have been the first time. (I see repeats every few months.) It's possible that it has more reviews because more people have read it.
Can't speak for the US, but the kindle version was a Daily and Monthly Sale here. That'll get some readers. And if we get a sale, the US usually has it.