I don't think it's so much about obscurity as it is about an arms race. Hashing algorithms are constantly being measured up against new exploit methods, faster cracking speeds, etc. It's a feature that we found collisions and other problems, not a bug.

A bug would be us continuing to use those algorithms without being able to mitigate their flaws.

The fact that we can find out that these functions are not as good as we hope and improve upon them is argument against obscurity. You can't do those things unless knowledge of these functions is common knowledge.