It failed for a number of reasons - timing, lack of compelling new features, IE's lack of support for application/xhtml+xml, Gecko's Yellow Screen of Death, etc. I'm not sure that you can blame any one of them. And it really wasn't a clean break in the sense that whyme is talking about.
I'm pretty sure it failed due to not being backwards compatible. Sometimes you can throw stuff away if it isn't getting much use, but backwards compatibility is too important in the real world.
If your browser won't browse the Web, consumers simply won't use it.
