I do not understand why it was not pursued.
Politics probably.
The rocket meisters just had too much to lose.
Did you know that galiLEO thought of it first : shooting cannon balls into LEO? Cannons were around in his day. He studied parabolic projectile arcs with ink-covered balls on a flat, sloped table with paper on it, and a sort of pinball machine spring-shooter.
There were no reliable clocks then so he timed things by his PULSE. Amazing isn't it? Such crude beginnings and yet he could dream of shooting cannon balls into space, IF only he had a big enough cannon.....
Now, 3 centuries later, we DO, the superconducting railgun. So sad, we knew how to do it TWENTY YEARS AGO, as a spin-off idea of the space based KKV(Kinetic Kill Vehicle). Why not do it on the GROUND? I remember Cap Weinberger(DEFSEC)having real trouble pronouncing Kinetic Kill Vehicle : conneticut...kinicktic....in a congressional hearing on star wars....
So, if YOU(NASA)were making $20,000/# to LEO with the shuttle to do 40 cents of work, wouldn't YOU try to smother the EMSL baby in the cradle? OF COURSE you would! It isn't "conquering the high frontier" that's important, numero uno is the BANK ACCOUNT!!!
Anyway, google ElectroMagnetic Space Launch, there may still be some info that NASA hasn't erased from 20 years ago....As I said then and I'll say it now : the only TRUE path to space is ELECTROMAGNETISM, the Coulomb FORCE. And may the FORCE be with you....
Well, no. There are plenty of technical barriers that can explain why it hasn't gone anywhere.