ga.js has no way of checking views on the internal tumblr dashboard.
Allowing such a screening would lead to:
Legal troubles under many (mostly european) privacy laws
[in a worst case scenario]
(i.e. 3rd party unscrutinized scripts like
ga.js running on the
Opening the tumblr dashboard site to a brand new daring world of XSS
attacks (tumblr board actually takes the
"no-scripts-on-the-dashboard" rule religiously)
[in a less awful scenario]
(i.e. 3rd party unscrutinized external images like
__utm.gif allowed to
appear on the dashboard)
Allowing advertising (also maybe phishing) from unauthorized rings on the tumblr dashboard.
Issues with the actual gathering of results: a typical tumblr dashboard contains content from 10 different parties, and the infinite scroll feature can push that figure up to 200 in just a few scrolls.
Also note that
ga.js and other trackers also have trouble tracking visits to the tumblr mobile version.
And yes most of this issues could be worked out, if Tumblr cooperated w/ Google.
But Tumblr isn't exactly a team player, and Google doesn't really care: Analytics is meant to track actual visits to pages that could generate advertising. Typical digital advertising: a banner, an adsense one, maybe, one that Google can monetize on.
Tracking views over the Tumblr dashboard may help assess the state of a viral campaign, but Google gets squat from that.