Many sites rely on Google Analytics to be able to do their own promotions and sponsorships, which is the only way they make money other than ads. By blocking GA, the site doesn't see you as a visitor. So, you use the site resources, don't see ads and don't add to their user/page view numbers. Plus, there's the fact that lots of sites use GA to handle inter-page click tracking so they can see what paths users take to analyze UI/price sensitivity/promos/etc and blocking GA may break your ability to actually use the site at all (many travel sites, for instance).

Would you block any analytics tracker - even one that didn't share data with 3rd parties? (i.e. a tracker that was purely to enable to site owners to gain insight into their visitors)

You can also use NoScript for that.

The vast majority of people use ad blockers to block ads. That's why almost no ad blockers block GA, etc by default. Plus, from my other comment: "Many sites rely on Google Analytics to be able to do their own promotions and sponsorships, which is the only way they make money other than ads. By blocking GA, the site doesn't see you as a visitor. So, you use the site resources, don't see ads and don't add to their user/page view numbers. Plus, there's the fact that lots of sites use GA to handle inter-page click tracking so they can see what paths users take to analyze UI/price sensitivity/promos/etc and blocking GA may break your ability to actually use the site at all (many travel sites, for instance)."

Some people just use adblockers to reduce the annoyance of looking at ads.

No, its main purpose is blocking ads. Those visibly (and sometimes audibly) annoying flashy things. It's in the name.

An incognito window doesn't use add-ins?

EasyPrivacy is enabled by default in current installs of uBlock on Firefox.

try right clicking on the thing, click uBlock link, paste:

## .post-sharing-button[href="javascript: void 0;"]

into the box (or delete the other text till you get that) and click create