That's part of the problem; they aren't charging you for the install, they are remotely tracking that you've done so and then billing the dev for it.
If you grab a cracked version, did the person cracking that game also remove the install telemetry, or did they just make it functional? Can you be sure?
In many cases, the dev would still be billed for you installing the game you didn't even pay for. Unity has no incentive to ensure each install is legitimate, as they profit from failing to catch that.