For a long time (twenty or thirty years) we've been asking, why
isn't hang gliding growing here in the United States? Why aren't more young
people joining our ranks?

There have been lots of reasons brought forth. Paragliding stole those
prospective pilots, it was too expensive, there were too few teachers, it was
difficult to learn, schools were far away, and the culture wars explanation: men
had turned into mice (with joy sticks in their hands).
http://ozreport.com/forum/viewtopic.php?t=29413

I might suggest that big changes, require big explanations and I consider the
big fall in the number of hang glider pilots a big change. Perhaps there was a
much bigger society wide change that was occurring without us noticing it. How
about the fact that men were just not earning as much money and that their
economic prospects had dimmed?

http://economix.blogs.nytimes.com/2011/03/04/the-struggles-of-men/

The Hamilton Project has produced a fairly stunning chart,
suggesting that median real wages for men have dropped significantly more than
is commonly understood:

The Hamilton Project said the blue line or full sample of men (which accounts
for reduced labor force participation) suggested that median wages had declined
by 28 percent, or almost $13,000 (in constant dollars).

http://www.hamiltonproject.org/papers/trends_reduced_earnings_for_men_in_america/

But in the mid-1970s, that pattern abruptly changed. Technological
change and globalization continued to power both economic growth and the total
earnings of the work force. Women, who were entering the market at increasing
rates, enjoyed the fruits of that prosperity in rising wages. But the fortunes
of a large segment of workers — male workers lacking specialized skills — were
unhitched from the engine of growth.

Over the past 40 years, a period in which U.S. GDP per capita more than doubled
after adjusting for inflation, the annual earnings of the median prime-aged male
have actually fallen by 28 percent. Indeed, males at the middle of the wage
distribution now earn about the same as their counterparts in the 1950s! This
decline reflects both stagnant wages for men on the job, and the fact that,
compared with 1969, three times as many men of working age don’t work at all.

Peaked in 1973.

Before the current depression:
http://www.nakedcapitalism.com/2007/05/it.html

http://www.nytimes.com/2012/09/11/opinion/brooks-why-men-fail.html?_r=1&hp

The end of men?
http://www.theatlantic.com/magazine/archive/2010/07/the-end-of-men/308135/
and the
book.