When they became too expensive relative to the average wage ...
In 1973, a SS Sub Date cost $385
Source:
http://www.minus4plus6.com/PriceEvolution.htm
In 1973, the average annual income in the US was approx $12000.
Source: www2.census.gov/prod2/popscan/p60-093.pdf
So, a SS Sub date cost less than 2 weeks pay (gross) in 1973. Not too unaffordable. Can afford to be used as a proper tool watch.
In 2011, average income was approx $45000
Source:
http://www.usatoday.com/news/nation/...me-table_N.htm
So, these days a Rolex Sub data is approx 10 weeks gross pay. ie 5 times the relative cost in 1973 making it a lot more out of reach to most people ....