I think the right question is: what happened 12 years ago?

The answer could be that the bubble burst.

I think there is a natural tail-off, but the 12+ year category rolls up this long tail into a substantial total.

"12+" is a wider bucket than "9 to 11".

The half-life of a software engineer is about 5-6 years. To understand this, keep in mind that most of "software" isn't working on cutting-edge problems using high-productivity languages. It's Java/C++ legacy maintenance and crufty business logic. A substantial fraction of law and business school students are programmers who landed in enterprise Java jobs and bored out after a few years.

management?

kids?