It's hard to hire. If it were easy, they wouldn't be reaching out to you with bullshit job interview offers disguised as job offers.

You have (presumably) a pile of expertise in this particular area that they will have to painfully recreate. Including the experience of having built this thing once, and all the lessons from doing so.

As the project maintainer, you get a privileged stream of insights into how other companies are using the library / tool.