Star Trek TNG and after uniforms (TOS had the women in minidresses for no good reason other than audiences wanting to see their legs), Babylon 5 Earthforce uniforms, Mass Effect - many science fictional designs for space navy uniforms are jumpsuits.
Of course, there are exceptions - the Star Wars Imperial navy wears something that looks more like a modern uniform, with the exception of armored stormtroopers and pilots.
The likely reason for the aesthetic is that we tend to think of flightsuits, but modern astronauts on the ISS wear pretty much regular clothing. Shorts and T-shirts are the most popular. Flightsuits might be worn under a pressure suit, but why would people wander around in a shirtsleeve environment in a jumpsuit. They're unflattering, they're awkward to deal with when you need to go to the bathroom, especially for females (Maybe that's the real reason StarFleet women wear dresses).
It seems far more likely that space uniforms would end up similar to current ones. So, where might a jumpsuit tradition come from?
Here's a possible explanation. Gravity.
Advanced starships are generally assumed to provide gravity for their crew by some means - spin, artificial gravity fields, whatever.
Current spaceships do not. The ISS is entirely a microgravity environment, although it's likely that the first spinning station will be constructed within the next 20 to 30 years. This means that astronauts spend days, weeks, months in zero G. This causes all sorts of problems for them and the mission, including the fact that an astronaut who has spent six months on the ISS can be, temporarily, as much as seven centimeters taller. That makes fitting into a suit to land difficult. Astronauts often get slipped discs when they return to gravity. That's aside from all of the other difficulties.
Several solutions have been proposed, but the most recent is something called the SkinSuit. The SkinSuit is a pressure garment, similar to a flightsuit, that simulates gravitic loading over the astronaut's entire body.
Of course, it's a one piece thing, a sleeveless jumpsuit.
It's very likely that after testing, astronauts on the ISS will routinely wear these things (Supposedly they only take 30 seconds to get off).
If we get a tradition of interplanetary travel in smaller ships with limited or no spin, then pressure garment jumpsuits might become what you wear every day.
And that could easily become a tradition that lingers long after the need for it has been dealt with.
So, there's a good explanation if you want to put your spacemen in impractical jumpsuits.