Artist's conception of travel through a wormhole (Credit: NASA)
Wormholes and other means of providing instant access between distant fixed points are narratively convenient. They make it possible to get characters from point A to point B without dying of old age en route. Wormholes (or their equivalent) constrain interstellar travel so that, for example, people cannot simply flee combat by going FTL, nor can they emerge above a planet before their photons arrive to carry out an unstoppable bombing run. From an authorial perspective, such constraints are very, very useful.
Once their attention had been drawn to wormholes some time in the 1980s, authors leapt on the chance to use them in fiction. See, for example, how frequently the phrase appears in American English.