That and also Modern Western Sci-Fi tends to wave away all the hard parts of engineering, politics, and economics when it comes to actually doing the thing.
How did Heinlein assume we'd colonize the Moon in "The Moon Is A Harsh Mistress"? Oh, don't worry. We just bootstrapped ourselves up there Ayn Rand style.
How did Kirk and Picard and Janeway find themselves on Galaxy Class Starships traversing the deep corners of distant space? Well, first we did a quick global super-holocaust because of genetically engineered racism (don't ask the finer details of that) and then we just... got better and turned Earth into a Utopia.
Maybe you buy into the more Posadist vision of First Contact, where a few starving refugees accidentally broke the luminal barrier with a rocket they assembled from spare parts. But the truly hard parts - the laboriously assembly and re-learning of scientific knowledge by each new generation, the failed bluesky research projects and dead-end engineering projects, the accumulation of trust between individuals within a state and states within the world necessary to mobilize materials and labor for these grand mega-projects - largely get breezed over.
An epic spaceship battle with the Trisolarians is, after all, far sexier to put on screen than a bunch of scientists grappling with the mathematics behind three spheres floating through space. So the old Asimov-style of SciFi as a series of entertaining word problems falls away, to be replaced by the Science Fantasy of Space Wizards and Warp Cores and Time Traveling Monkeys.