Autodesk’s mobile offering started to appear about 3 years ago so, obviously, they did not have much choice in what they targeted. That focus continues, I think, because they don't have much to offer in the respective desktop environments (Mac, Linux), and want to maintain some presence in those camps.
For the most part, their current app lineup scales as would be expected to these mobile devises. Which is to say the functionality is directly proportional to processor power. Most are standalone apps, some integrated for downstream processing (those tend to be Web, thus WOA, accessible).
Public statements to explain their (Autodesk) decisions remain elusive, so we are left to speculate.
It could be that Autodesk refrained because they felt their Windows presence was already sufficient. They may also feel that Mobile devises are cheap enough that even a Microsoft based enterprise could afford to sprinkle a few iOS/Andoids into the mix. Plus, they may have bet on Intel devises, and just decided to save any additional development costs.
Earlier this year I had hope that their WOA offering was in the works but, due to a higher level of desktop integration and consequent higher complexity, was slow getting to market. That prospect looks grim at this point.