Tube question

I'm new to tubes, but there is a couple of things (well more than a couple, but for now): Why, with all of our modern technology, is it that we cannot make a tube with the sound quality of the ones in the late 50s to early 70s. What was it about that time, that we cannot seem to duplicate that quality today. I never, when hearing the scoop about great tubes, hear any new tube manufacturers being mentioned. Are there Chinese, Russian, American or the like, companies making very high quality sounding and constructed tubes? thanks in advance. warren