Adding the format seems to be easy, the problems lie in the quality assurance of every file being inspected for good isolation and transparency which in the large pool could be anywhere from perfect to horribly done.
For 3D renderings its a no brainier, I really cant get around the idea of not using a perfect alpha channel when its clearly available since over a decade ago at even the simplest computer user and installation.
In short, costs money to check these files and they didn't see enough financial benefit in the end compared to the adoption and use by clients.