<Controversial opinion> Computer scientist and mathematicians love lisp/scheme, everyone else hates it. The problem is that the syntax, concepts etc are so different that you really have to learn the language to make even small changes. Just reading prefix notation takes quite a bit of adjustment. When I was using emacs doom every time I changed my config felt like stabbing in the dark (hence I moved away). In contrast I could make lua changes (without any prior lua knowledge) without any problems.
I don't want to learn a new language just to configure my editor.
So by choosing scheme they essentially say this is an editor for computer scientists only. </controversial opinion>
Lisps make great configuration languages because of how dynamic they are. It's like Javascript on steroids. Redefine core symbols. Modify a syntax form and reevaluate all of your code so that it does one thing in one environment and something else in a different one. When building large software in a team this can be a big drag; learning some weird syntax form that a coworker merged in that you didn't review can be a headache and when everyone makes their own design patterns, the codebase becomes a mess.
But when you're just configuring software this heavily dynamic nature becomes a strength. I just need to build the abstractions in my config that I need, nobody else. It's easy to poke around in and spend a few minutes writing and iterating on code to get the config I want.
I agree that the prefix notation and the soup of parentheses give it a higher learning curve than something like Lua which is easily understandable if you have experience in pretty much any modern programming language. But it's not the mathematical/computational purity that makes Lisps appealing, it's their highly dynamic nature.