Because in my humble opinion, they would make for interesting special weapon types (like the kinds you can get from STFs and FEs). I would highly doubt they would run out of new weapon designs for a long time if they drew from these concepts, which they've had the right to since they took over the STO project.
Looking at the 8th option on the concept chart... holy crap. The designs are alright, but not very Trek. The stuff we have now is exactly either, but it's better than that stuff.
Although I must say I do like the revolver bit.
I admit, I was wierded out by that one until I noticed that it has some kind of thruster to make up for the extra weight. Seems a bit wasteful of power needs, though.
If by Trek you mean something you could see Starfleet making standard issue, I agree that these weapon designs don't look that AT ALL. Some of them would make for some rather interesting non-standard/non-Starfleet weapons, though.