They block applications that interfere with the operation of other applications.

This would include an ad blocker that blocks ads in, say, a free game, or the built in Chrome browser.

The common workaround was to run connections through a VPN and your ad blocking happens there. I'm not sure if they started cracking down on that as well.

Having apps that modify other apps can certainly be desired behavior, but it's clear why there would be legitimate concerns about customer security in allowing apps that can do so.

Don't other platforms block apps that either are too close to existing functionality or interfere with the operations of the builtin apps?

Sure I was just pointing out that they do exist at least as far as I could tell.

On iOS I use Focus and Safari and that has been pretty good for me. Obviously that's not something that would work on Android.

So... why is it possible?

There are three approaches:

1. Create a browser with ad blocking builtin or possible with addons (like Firefox).

2. Create a local proxy that blocks ads, and make the user configure it as the system proxy.

3. Require root privileges and do whatever you want (2, or maybe change /etc/hosts, like AdAway does). Yes, there are tons of apps in the Play Store that only work with root. Google never cared much about them.

They do, yes. What you've linked is a browser with ad-blocking capabilities, which is treated a bit differently. What they remove are ad-blockers which block ads in other apps.

And you can still get them on Android, but not via the Play Store. You have to go through third-party stores such as F-Droid, Aptoide or Amazon (or just directly download the installer-file off of a webpage).

http://www.androidpolice.com/2013/03/13/breaking-google-has-...

Chrome for Android doesn't allow browser extensions, possibly to prevent adblockers from being used. But that's a separate issue.