Public goodwill is a thing. Also, their offer was lackluster. But with Youtube Music being a part of Premium and getting better and better overtime, more and more people are actually on the lookout for signing up. There's also a psychological aspect of it. Remember how it feels when you're just about to do something and someone told you that you have to do it? Taking the agency and initiative away tend to annoy people and have an adverse effect on the task. You might not be personally affected by it but it's a common thing.