I thought we all had discussed this in another thread... The point is to make everything uniform, as mixing 0-index and 1-index based features is too confusing, there would be MANY errors on the game developer's part. Imagine bug requests "MY GAEM NO WORK WYYYYYYY" etc. and it turns out some object is using different indexing etc.
You can always add -1 to the 1-indexed stuff to make it 0, but that'd be complicating it needlessly. Sometimes we have to agree on a standard to stick to. 1 indexing is the chosen one.