For every successful product, there's at least 10 free tools that do the same thing (or something similar). It's not crazy at all - people (in particular larger companies) need support, assurances the product will still exist/be maintained in the future, etc. A lot of people will pay you just so they have a human on the other side of the line to talk to, in case things go wrong.
Never used Sidekiq myself, but I believe its value is mainly speed and reliability. It suits systems with hundreds of thousands of jobs to process. At least that's what I read on website :)