It's not totally absent, but usually rare.
I have four PCs in three different games, out of around two dozen characters in various games, with a romantic interest. The two olders are in Ars Magica, where you have several characters and use one or the other depending on the situation. To integrate them both in the covenant (it was a Spring Covenant, nearly noone outside of the PCs), I chose to make a Merinita mage and his feyblooded wife. Then, in a Vampire game, a weird gangrel (who happen to have found a way not to be damaged by sunlight) and a NPC witch. It's rather a platonic affair than a torrid romance, with a bit of paternalism from my character. When we found a weird orphan that don't seems to have had parents
at all, it began to be a sort of Addam Family thing.
The last one is in D&D. We decided to make a campaign where all PCs would have strong ties. We hesitated between family ties (all from the same family), childhood ties (all multiclassed something, with the same master for the Something class), geopolitical ties (all exiled from the same distant country, and seeking fortune for revenge).
We ended up with merging all three: my character as a sorcerous princess, her sorcerous husband of lesser nobility, her sorcerous brother-in-law, and her less sorcerous sister-in-law. Exiled from the same oriental realm due to the failed plotting of my character's father.
We would not use this kind of thing to gather the party in all campaigns, but doing it once is interesting. These were our most fleshed-out characters, as we had the possibility to create our character's motherland, derived from pseudo-Japan and pseudo-China, with some other pseudo-countries thrown in, its customs and traditions, some family quirks for the aristocracy, etc.
Family ties, romance, political ambitions, exotism, action: all ingredients of adventure !
