Although I don’t like Flock, I’m a bit skeptical of the claims in the article. Most screenshots appear to be client-side JavaScript snippets, not API responses from this key.

In the bug bounty community, Google Maps API key leaks are a common false positive, because they are only used for billing purposes and don’t actually control access to any data. The article doesn’t really prove ArcGIS is any different.

Security for maps is basically impossible. Maps tend to have to be widely shared within government and engineering, and if you know what you're looking for, it's remarkably straightforward to find ways to access layers you would normally have to pay for. It's a consequence of the need to share data widely for a variety of purposes -- everything from zoning debates within a local county to maps for broadband funding across an entire country create a public need to share mapping information. Keys don't get revoked once projects end as that would result in all the previously published links becoming stale, which makes life harder for everyone doing research and planning new projects.

Moreover, university students in programs like architecture are given access to many map layers as part of the school's agreements with the organizations publishing the data. Without that access, students wouldn't be able to pick up the skills needed to do the work they will eventually be hired for. And if students can get data, then it's pretty much public.

Privacy is becoming (or already is) nearly impossible in the 21st century.