When I got into Grav Theme Development more than a year ago, I didn't like how it does not really work to try out themes, given that there are no enforced rules on what templates you need to support. And it appears that to actually deploy the look the theme advertised, you need a particular kind of page organization. And again, this isn't transferable across themes. A client will have no means to shop and switch around. You wouldn't either, unless you are a coder and tinkerer yourself.
I stand by the principle of loose coupling still. But when it comes to doing client work, it is not enough to build a loosely coupled theme. You also need to hand over the client code in the most convenient way possible. Grav, being a flatfile cms, excels here in that you can simply drag, drop, and extract a preconfigured site into shared hosting.
Skeletons reflects this ease of handover. You can also pre-configure the site yaml to include business details so that your skeletonized theme calls from that part instead of calling from a specific page frontmatter (although this is an equally valid config as well). I've seen old Grav skeletons implement this variation (it never really carried out into future themes). Clients availing of bespoke web services aren't really in the business of dressing themes on their own web design; they want you to make it convenient for them to get them the look and functionality they want. So make it convenient for them with skeletons.