Advancements do not just stop.
There are ALWAYS new things to explore and technologies to develop.
The apparent slow-down of technological discoveries (mainly being stuck on Warp drive for example for a long time) was the unwillingness/inability of writers to do it (along with other things).
That's the insular assumption Westerners make, that the current conditions of our society are a universal constant for all time. But history says otherwise. Progress is not a constant, but varies depending on the society and the era, influenced by factors like the social structure and values, the availability of resources, the incentive for change and growth, etc. Many societies value stability more than change. Many societies turn away from valuing science and innovation. Hell, look at the extreme right wing in the United States and how hostile it is to science and scholarship. Look at how many members of the Congressional Science Committee are Tea Partiers who don't believe in evolution or climate change or, heck, the Earth orbiting the Sun for all we know. If they ever succeeded in taking over the country completely and imposing their values, then progress in the US would go into reverse and we'd end up being a Third World country mired in superstition (heck, we're halfway there already). So there's no guarantee that even the most scientifically progressive and open-minded society will stay that way indefinitely. That's just one of the possible states a society can exist in.