It has been ZERO DAYS since some GPL'd software made me "agree" to the GPL while installing it.

The GPL is not that kind of license: You don't need to agree to it. Agreeing to it changes nothing.

This just happens because installers have a premade "license" page and the GPL license seems like a natural fit.

But there's no point: You need to notify the user the software is GPL, but that's all.