Tech generally disappears (though it never/rarely really does completely) either because it proves not viable/economic, or it's superseded. Though sometime it's

Tech generally disappears (though it never/rarely really does completely) either because it proves not viable/economic, or it's superseded. Though sometime it's because of shifts in fashion, or legal/moral restrictions. Hyped then didn't take-off: persistent ram (mram, Feram, PCram etc). Superseded: Incandescent lightbulbs, gas mantle tech, CRT display tech, vinyl, cassette and especially CD/DVD tech, etc. Fashion: maybe teasmades (alarm clocks that brew tea), I'm sure there are better examples. Legal/moral/health restrictions: maybe 'consumer' radioactive tech, radium clocks etc.