Because if it is the end user, the strong version of the argument would be as follows: The end user signs a document, baked in is an attestation that Google guarantees that this device is an approved Android device with a clean boot chain and a Chrome web browser. Then the end user contests the signature in court, either because they didn't understand what they signed, or they did not sign it at all, or did it under threat. How could the attestation help here?
I do not have experience with all EU countries, of course, but more than one, and nowhere is this an issue today. Countries use a wide variety of electronic identification, from soft certificates and mobile phones to smart cards. But as far as I know, all countries accept signatures made even with normal Windows PCs. You can contest a signed document in court for a multitude of reasons, but that's not specific to electronic signatures.
So they're just going to use the Apple/Google standards and declare the job done. So it's theater from all sides. Politicians will pretend this is a good solution because they don't want to spend real money, and they really want to tempt EU kids to get loans on their smartphones because, you know, in the EU you're protected from companies exploiting you. Of course, that just means governments will have to do it instead.