The current copyright law is unsustainable. Pretty much every melody you can think of is copyrighted and as an artist you can be anxious that anything you make can be claimed by someone else. Copyright laws need urgent change as they are not fit for purpose...
In this case that's not the problem. Beethoven isn't copyrighted, but public.
If the law promotes, say by making it a default, that one side can easily benefit from a certain behaviour, then people, companies will assume that as the behaviour to favour. And then these are the consequences: that going around claiming rights on whatever you feel like is not only not punished by Youtube but carelessly accepted. Because it's just easier, less effort.