[lxgr]

The technical background is that Android allows marking certain GUI surfaces as "sensitive", which increases their in-memory protection somewhat (not sure to what extent) and also makes them inaccessible to various remote screen recording/capturing solutions, including adb.

Not being able to take a screenshot is more of a side effect of that, but is arguably the main reason for most apps to use them in practice.

It's also been around for many years.