GoodJob author here.

The core reason I wrote it was to see how lean/simple I could write a database-backed ActiveJob adapter today. And hope

In practice any adapter should _just work_, but also all the other adapters pre-date ActiveJob (Rails 4.2) and Concurrent::Ruby (adopted in Rails 5.0 I think). The assumption is that building GoodJob on top of what already exists in Rails today, it can be performant (enough) and simple (easy to understand, maintain, keep compatible with new versions of Rails, etc). That's not a big claim, but maybe it's compelling.