I've commented above that this seems like a bad approach, but it sure feels like a lack of awareness vs. an intentional dark pattern. The internet makes it so easy to assume the worst but I think this is a case where we should start with the most charitable interpretation.
Dark pattern? Pro plugins are built in the same way as is accessible to any user. What's the real issue?
That you have to go looking, actively, to realise there is a paid option.