I think the reason is they have a bunch of ephemeral hosts which they don't want to put in a central web interface or collect statistics on.
They are only interested in getting some insight as to what went wrong with this host so they can fix it in the future.
Vector is for per-instance custom drilldowns. I gave a talk last year where I showed how they both fit together: http://www.brendangregg.com/blog/2014-09-27/from-clouds-to-r...