Well, until recently, I doubt iPads had the power to support a good multi-track video editor. More recently I’d guess that companies with the resources to tackle what would be a big and probalby expensive project like this don’t see enough profit to make it worth their while.
With the new iPad Pros, and Apple pushing to present the iPad Pros as a profesional tool, that might change. But I doubt it will be this year, or even next.