It's also loud.
I don't need or want everyone sat in the same room as me to know every little thing I do on my phone. Leaving aside things that are actually private, that's just a level of inane garbage that we all don't need to know about each other.
Sometimes I just want to glance at the football scores without announcing to everyone: "OK Google, what is the current score for the football match between Swindon Town and Harrogate?".
Edit: It's currently nil-nil, if you're wondering.
It probably isn't legal most places. EULAs are already considered fairly flimsy in terms of enforcement, but changing an EULA after you've already bought a device, in such a way as to reduce your statutory rights, is almost certainly a complete non-starter.