I've got a quick-hitting post for you today, mainly to put this super-cool graphic from the Wall Street Journal in front of you.
The takeaway is that while it used to be pretty simple to generate healthy returns by simply buying and holding bonds, that dynamic has changed dramatically with today's microscopic interest rates. Part of this has been intentional, as central banks around the globe have purposely driven interest rates lower in an effort to get savers to take more risk with their savings (which in theory, would stimulate greater economic growth — a hotly debated premise that many feel is false and needlessly harmful to savers).
As savers have been required to "reach for yield" by venturing into riskier parts of the investing markets, not only does complexity increase ("I used to just own bonds, now I have to own other stuff too"), risk also increases. That's shown by the growing standard deviation numbers, which as the caption indicates measures the "likely amount by which returns could vary."
So if you've felt over the past 5 years or so that investing has become more complicated, you're not wrong. SMI hasn't added new strategies and encouraged readers to build more robust portfolios combining multiple strategies just to have something new to write about. The need for new approaches like Dynamic Asset Allocation have been driven by the changing investment environment — specifically, the massive reduction in "safe" yield available from bonds.