NPCs in RPGs perform two very important functions. First, of course, they serve plot elements to the player through the PC, telling you that something needs doing, or the reason why a thing is the way it is, or where to find the dweomered dingus of doom. Secondly, they hold a mirror up to the player character, allowing the player to perceive his or her character the way an in-universe personality does.
It is in the second function that an NPC romance really takes on a unique role. While some games provide an option for the player character to have a sex scene or even get married, this is often simply a forgettable moment thrown in for a laugh, like Geralt's many conquests among the ladies of negotiable affection who so densely populate parts of the original Witcher game. A true NPC romance however, requires developing a personality for the paramour, and a relationship between that character and the player's. When well written and executed, that relationship becomes emotionally real to the player and triggers empathy and pathos, so that you, the player in the real world, actually care about the fictional character you see "falling in love" with your avatar in the game. Nothing else in the virtual world has as much power as these feelings to engage the player in the world, in the player character, or in the story of the game. It bypasses your critical thought and speaks directly to your humanity. A bromance (like with my best buddy Garrus) can come close, but a romance really gets past your defenses better than anything else, in the game just like in life.
This gives the writers the ability to make you believe, for example, that your character is really great. If you let yourself love Ashley, and she tells you that she believes that you can beat Saren, you believe it, too. In the same way, if the love of your virtual life is uncharacteristically afraid, it adds to your sense of suspense. Engaging the player on an emotional level though the PC is magic. It makes the fiction of the game take on a measure of reality, because in a very real sense whatever you can feel, exists.
This emotional dynamic also makes the scenes associated with it memorable. The moments that you actually feel in a game are the ones that you most remember months and years later. One of the most memorable scenes to me from any game, ever, was the redemption of Bastila in my first playthrough of KotOR. I started flirting with her because it was funny, but by the end of the game dozens of hours later, I was really surprised to discover that I actually cared about her a lot. When she finally confessed her unreserved love for my character, when she looked out of my monitor and said "Nothing could make me feel safer than to be loved by you," that was the moment that I won the game. Going on to battle Malak, I felt like I was indestructible and the outcome of the fight was inevitable, a formality.
So, no. There is not too much focus on romantic sub-plots in BioWare's games. They are a small fraction of the game's content that make the rest of it feel much more real, if you let it. They're worth it.