Arbitrary sorting can be really useful for relatively short lists, like a todo, but seems to me to be a lot less useful for thousands of items. And most cases where I would want that, like grouped by topic, is a better use case for tags, or the topic can be included in the title and work with alphabetical sorting.

But good news, niche requirements can be satisfied on both platforms by writing an extension!

Obsidian has the philosophy that the filesystem is the source of all truth, and it's showing directly the filesystem without any obvious layer in-between. The reason is, that you should be able to read your data with any other app and have the same amount of data accessible. So from their POV, there is not really any place to store the information for the sorting. Adding it to the filename, would annoy the people, so It's up to you to choose your own plugin allowing this.

Also, with the new bases-features, you can easily create your own sorting with a table, or whichever view you prefer.