I do find it a little hard to believe that we'd be stuck in one system for that long, isolated, without trying to go somewhere else... and not finding a means of doing so...
I believe at the time of the Lucifer explosion the only canon known jump route was Sol - Delta Serpentis
In 2335, the destruction of the Lucifer superdestroyer collapsed the Sol jump node in Delta Serpentis, severing all contact with Earth
you would have thought that in the time before the explosion any other jump node usable in system would have been found, it is even loosely suggested that detection of usable jump nodes is a simple matter so if they cant be detected they cant be used.
on developing new technology there is 2 avenues to approach this
1) New Technology
a) Develop a Knossos style devise.
Petrach mentions it could take over ten years to build a similar device and that is with the resources of the GTVA and Dr. Hargrove's research which Earth has neither
b) Development of a new FTL technology
Again this requires resources that Sol either has less of or could lack entirely a situation less likely than in the GTVA
2) Improvement of subspace-drive technology to alow the use of unstable nodes
naturally the efficiency of subspace drives and their ability to handle unusual circumstances would improve but this would happen slower than in the GTVA as the GTVA has more usage data to go on and more test locations so the GTVA is more likely to reach Sol through unstable nodes
