I want to know what they do with the data
We use it to see plugin/theme popularity, track adoption rates of new
WP versions, and get a feel for the platforms that people run
WP on. For instance, knowing how many people run PHP 4 is very helpful in deciding whether or not to drop support for it.
why they refuse to make it non identifiable.
A URL is a standardized, globally unique, verifiable identifier for a WordPress site. It is not disclosed, per the privacy policy. Indeed, our tool for viewing this statistical data has only numbers and percentages — for instance, the number of people running MySQL 4 vs MySQL 5, or the number of active installs of a particular plugin. We don't have a "see what site X is running" tool. The purpose is to make better decisions about WordPress development by looking at the aggregate data.
If you're uncomfortable with this, there are plugins available to obfuscate the URL you send (though obviously it cannot obfuscate the IP address your server sends, unless you're willing to turn off update notifications altogether).