I think it's due to the fact that technology development has become more focused on efficiency than anything else. SST may have been fast, but were they fuel efficient? Cost efficient? High safety rating? Affordable for the populous majority? All of these things and a long list of others are the primary focus of new tech.
"It gets you there faster" just isn't a good selling point anymore. Products that put being cool and trendy (or in this case, fast) over being efficient don't sell as well as they did in the 80's-90's, because "cool and trendy" might as well be replaced with "$$$ EXPENSIVE $$$".
It just doesn't work with the state of our economy. People are also becoming more market savvy, and more aware of what one thing or another is ACTUALLY worth, compared to the price tag.