Because that is all the technology there is.
Your assumption that technology is going to somehow develop ad infinitum is not based on any evidence. We have no examples of technology more advanced than what we have now, and it is entirely possible that technology simply cannot develop much beyond what we currently have.
Just because technology had an anomalously rapid advance last century does not imply that similar advances will continue into the future. Last century was an anomaly, not a trend. before last century, technology scarcely chanced over hundreds of thousands of years. In all likelihood it has now stopped advancing.
Try to see rockets as mature technology. They have barely developed over half a century. This is typical of most technology. It goes through the phases of discovery, rapid development, maturity, stagnation. Different technologies mature at different rates, but eventually they all do.