What makes you think we don't?
A person close to me worked security for Los Alamos and Sandia Labs. Being a science geek, I used to (annoyingly) pump him for even the slightest glimmer of what they were working on. This used to piss off this person to no end. One day when I asked him about something I had seen on the web, he said:
"Think of what you think we have, add a hundred years of research and development, and you start to come close."
The late Ben Rich, the second head of Lockheed Skunkworks after Kelly Johnson, has been quoted to say three things right before his death in May of 1995.
1 : “Inside the Skunk Works we were a small, intensely cohesive group consisting of about fifty veteran engineers and designers and a hundred or so expert machinists and shop workers. Our forte was building technologically advanced airplanes of small number and of high class for highly secret missions.”
2 : “We already have the means to travel among the stars, but these technologies are locked up in black projects, and it would take an act of God to ever get them out to benefit humanity. Anything you can imagine, we already know how to do.”
3 : “We now have the technology to take ET home. No, it won’t take someone’s lifetime to do it. There is an error in the equations. We know what it is. We now have the capability to travel to the stars. First, you have to understand that we will not get to the stars using chemical propulsion. Second, we have to devise a new propulsion technology. What we have to do is find out where Einstein went wrong.”
We Now Have the Technology to Take ET Home
https://www.youtube.com/watch?v=u9ZZekWMiUQ