We didn't go through the W3C or the IETF to develop RSS. It's not that we didn't try. Neither organization wanted to build on our work, and RSS was already a very popular standard, and all either organization offered was to rip it up and start over. That wasn't an option.
So the RSS 2.0 spec lives on a server at Harvard University. An institution that has been in existence since 1636, predating Google by several centuries. An institution at least as respected as Google itself.
So why does Google ignore the spec? Why do so many of their applications fail to process feeds that are permitted under the spec, for very good reasons. Why does Google so thoroughly disrespect work that has proven so useful and so popular?
I don't expect to get an answer, and I'm pretty sure I don't even want to hear it because it's sure to be ugly and egotistic and very very BigCo. But it's awful every time I try to view a perfectly legal feed in Chrome, which is the browser I use these days, and see it mangled because someone at Google thought their opinion was more important than the installed base.
Jon Postel was familiar with this problem when he proposed what has come to be known as Postel's robustness principle. In this case, being "liberal" means "implementing the spec."