In part at least, blame Google and Bing. It's not the storage space or bandwidth. It's that you're expending a lot of time and money--sometimes literally in the case of paid search--to surface mostly the most current and relevant information. Personally, when I search for the fix to some problem I'm having, I rarely want a 2010 article about my problem and usually get mildly annoyed when I get one.

And technical content is just part of it. Companies have current things they're selling, marketing, and messaging. They don't want that all mixed up with whatever they were doing five years ago.