Even when producers do try to build something it doesn't always work. Take Worf/Troi for example. That had ample buildup in season 7 of TNG but it didn't really work because there was no romantic or even sexual chemistry between Dorn and Sirtis. So even though they built to it the pairing still didn't work.
I also point to DS9 and Odo/Kira. That was built to for a good five or so years before it happened and there was pretty good chemistry between Vistor and Auberjonois but once they got together it all sort of fizzled. Odo/Kira worked together as an unrequited romance.
On the other hand I thought the Trip/T'Pol pairing on Enterprise worked though I thought the build to that was pretty hamfisted and obvious.
I also enjoyed the Worf/Jadzia and Riker/Troi 'ships. I had been rooting for Worf/Jadzia since before Worf ended up on DS9. When I first saw Blood Oath I realized that Jadzia and Word would be perfect for each other and cursed the TV gods that they were on two different shows and such a coupling could never take place. Who knew?
The Riker/Troi 'ship was handled clumsily in the TNG movies but Frakes/Sirtis had such undeniable chemistry that I thought it made up for all the writing deficiancies in those movies.
At the end of the day I don't really think Trek handles romance all that well. It does a damn good job about romantacizing space exploration and adventure but it really is shit at 'ships.