Couldn’t I just put my name and address on a label?
Sure, but then it wouldn’t be private.
The more personal information you put ‘out there’ the more likely you are to receive unwanted messages.
If you put any personal details on a key ring, then lose it while travelling, whoever finds it has your keys, and knows you’re away from home for a while. If those keys never show up, you’ll know they’re still out there, somewhere. Isn’t it worth securely tagging them to avoid that risk?
You could use an email address or phone number instead. But if those depend on you staying with your current ISP or mobile provider, or employer, then leaving any one of those renders all your labels useless.
Your WhosMyOwner tag is yours for as long as your account is active, and changing your contact details has no effect on it (just update your account when you can).