[1] For example the find-replace dialog closes itself when I press "Replace All", as opposed to other editors I've used where it doesn't. It's annoying to have to reopen the dialog after every different search.

The other benefit is that if the company dies you know you wont have wasted all that effort with the editor because open source editors don't live and die at the behest of the company that started them.

Think of it as insurance for one of you most important tools.

I haven't changed anything in core, but having the ability to walk through all the code is super useful in debugging.

More than 1144: http://blog.atom.io/2016/05/06/two-years-open-source.html

You care about the utility of your editor, and that's fine. Several other comments here try to highlight ways in which open source projects are more pragmatic, like the ability to make modifications yourself or take advantage of community contributions.

All of that is just arguing about utility, though. For many people open source is a moral issue. RMS is a notable example here. And I prefer open source tools for this reason.

If you believe open source software is morally superior to closed source software then the utility considerations are of secondary, or perhaps even zero, importance.