I'd say Dojo is much closer to YUI in scope and purpose. As to why it's not more popular? Likely marketing. Dojo isn't sexy. It's been around for a very long t

I'd say Dojo is much closer to YUI in scope and purpose. As to why it's not more popular? Likely marketing. Dojo isn't sexy. It's been around for a very long time. You'll notice that a lot of discussions around things like module loading reference Dojo as an inspiration.