I'm not sure about the German market for craft, but American craft can almost certainly be traced back to Frederick Maytag's purchase of San Francisco's Anchor Brewing in 1965. Since then, 'craft' or 'microbrew' grew slowly through the years.
A lengthy but interesting report called THE MARKET FOR CRAFT AND SPECIALTY BEER, A Market Intelligence Report, March 1997 has an impressive description of why craft in particular was able to keep growing, and why it wasn't labeled a 'fad':
"There is also a floor under the craft/specialty segment. This is not
a fad segment like packaged draft, dry, ice, clear, or perhaps even
red. While growth in the craft segment will slow, it will not peak
quickly and then lose share, as the fad beers have. The
craft/specialty segment has firm underpinnings from homebrewers and
other beer aficionados. Many of the homebrewers prefer to brew their
own beer (done right, it’s even better than the best of the craft
brews), but they often sample commercial brews to try unfamiliar or
difficult-to-brew styles, and of course they’re top prospects for
drinking craft brews when they are at a restaurant or brewpub."
That explains a lot through the 90's, but why the quicker increase in growth patterns in the last 10 years?
According to the Brewers Association (a US-based trade group):
"Between 2011 and 2013, 80% of craft growth came from new craft
appreciators, the majority of which were in the 21 to 29 age group,
and their impact is still muted. Lester Jones of the National Beer
Wholesalers Association (NBWA) sees Millennials as not fully
economically activated yet due to the impact of the economic recession
and their struggle to transition into aging Baby Boomer jobs. This
means as the economy improves we should feel the impact of the
Millennials even more. The message here is the fastest growing and
most influential demographic is also moving the fastest toward craft."
Pair this with the increased ideals behind "Trade-ups and premiumization", and you have people willing to spend a little more to gain an perceived increase in value and quality.
IBISWorld shares that craft beer has enjoyed a 19% growth in the past 5 years. I don't know about you, but that's incredible considering the economic woes of developed nations.
It appears to boil down to a long, slow pattern of growth that has reached a massive generational shift in consumption which has caused a spike in sales volume, which in turn is pushing every store from New Jersey to Frankfurt to attempt to capitalize on one of the few growth industries.