Product innovation asks what to build. Business model innovation asks how the whole value engine should work. It reconsiders who the customer is, what they pay for, how the offer reaches them, and where margin comes from. Shifts to subscription, platform, or outcome-based pricing are classic examples.
It is harder than product change because it touches the operating model, not just the roadmap. That is why it benefits from structured method: patterns, canvases, and a disciplined way to test assumptions before committing.