Longman Dictionary of Contemporary English
sunset industry
noun
EXAMPLES FROM CORPUS
▪ In such circumstances, an industrial policy that seeks faster and more efficient rationalization of the sunset industry may be advantageous.
Wikipedia
Sunset industry
A sunset industry is an industry in decline, one that has passed its peak or boom periods. As one example, analogue recording technologies for audio or video have been supplanted by digital equivalents; although analogue equipment is still offered, sales have declined dramatically and are not expected to recover, so this segment of the market has been branded a 'sunset industry'.