I'm sorry, why does this paper have only 689 citations and not ten million? www.mindmeister.com/generic_file...

Another possibility: it does have many thousands of citations, but only a fraction of old papers were digitized (common problem with historical data) and thus Google doesn’t see them

Lots of older papers don't get read because they are not available online (a hypothesis that relies on the assumption that people read papers before citing them)