The justification is complete nonsense. The claimed goal is to reduce the amount of plastic that ends up in the ocean. But I fail to see how the straw used to drink a cold chocolate in a restaurant in Vienna could ever end up in the ocean. So the basic premise does not seem to be very well-reasoned. Maybe I'm cynical, but I cannot get rid of the suspicion that this law is mainly about virtue signalling. It seems to be designed to maximize PR impact: they chose a topic that everyone agrees with (saving the environment), that everyone understands, and that does no serious harm to any politically powerful entity. Well done, micro-managing overlords of the European Commission!
Just because your properly-disposed straw in Vienna won't end up in the ocean doesn't mean the bill doesn't accomplish its goal of reducing ocean waste. It just means the bill has wider-reaching impact than its stated goal.
If that wider-reaching impact is, more generally, to reduce plastic waste as a whole... then I'd say this is great.
Given the amount of people who think like you, though, I'm quite glad the EC is micromanaging. Reason is hard to come by.
The problem is that by micromanaging, the commission violates the principle of subsidiarity. This is not the first time and I generally don’t have much trust in anyone who disregards his own stated principles whenever convenient.