One reason why intranet ROT becomes such a problem is that staff write web pages as if they were memos. Now, memos hit the desk every day, and one memo often cancels, contradicts or expands on a previous memo. Staff understand this. They read memos in the context of other memos.
Memos are not intended to be the last word on any subject: they are part of the running commentary on business and office life. They arrive as part of a series, and are only sent to the people who need that information (or that's the plan). They are usually read on the day they arrive or soon after. And they always carry a date.
Many everyday writers seem to subconsciously assume that intranet pages are similar. But they are not. Intranet pages have no sequence, may not even be found (let alone read), can be viewed by anyone, can be read months or years after the date issued, and often don't carry a date, though they should. And unlike memos, an intranet page should normally be the only, latest, authoritative version of a topic on the entire intranet. Otherwise people get very confused. (Exceptions: news, media releases, newsletters, blog entries, and so forth.)
Memo-writers assume that outdated information online can be amended by adding a new intranet page, or adding more information to an old intranet page. Soon there are five pages on the same topic...
Content writers don't do this on purpose. The effects can be minimised by experience, a rigorous workflow system, and smart information architecture.