That's not really the case. Getting to the space stage is fast, but that's where the game pretty much begins. There's a lot more to do then than the earlier stages, communication with other species is much more developed, as is the management of your empire. Warfare is also more complex. For example, if you need a planet, you can just fly down to the planet and destroy every city until all sentient life is eradicated and then claim the planet, or you can just blow the planet up with a giant laser, or you can reverse-terraform it by purposefully applying the wrong terraforming tools, or you can just crash a giant asteroid into it. Or, if you're not feeling particularly violent, establish a trade route and eventually buy the star system. The galaxy is huge (approx. 500 000 stars), so the game pretty much never ends at this stage. The end goal is to reach the centre of the galaxy, which is protected by a very powerful empire that declares war on you for violating their territory, but besides that it's really a free game with no defined goals besides general expansion.