Hey Eric,
I'm happy to have this discussion and provide as much info as I can about why we use dojo. I've tried to imply this, but I think I need to be more clear: popularity should not be the primary reason for picking a tool/framework/technology.
jQuery is not the right tool to build our mapping API. It provides a great DOM API, event management tools and AJAX tools. That's it. It's missing a number of things which we would prefer to not re-invent.
One thing I'd like to see is a write up of things that dojo does poorly and could be improved by switching to jQuery. There's plenty of vague dojo bashing, but that doesn't go very far as to making a case for switching from one framework to another. "Dojo sucks, jQuery doesn't" and "everybody else is using it" are not persuasive arguments. And the latter isn't true in the online mapping space.
Regarding other open source mapping options, the only one I know of that uses jQuery is jQuery Geo (which is still in alpha, at the time of this post). The rest, Leaflet, Polymaps, OpenLayers and others I'm probably forgetting, don't use a framework. So if you want jQuery with those, it's up to you to include it.
At the end of the day, it's all JavaScript. I think our time is better spent getting to know the language, our tools and how to make cool stuff rather than holy wars over which framework is best. I'm hoping you'll give our API (and dojo) a fair shake rather than dismissing it solely because it's not built on jQuery.