Just a matter of priorities. The workflow you mention has a good enough workaround available. (See Hierarchical or flat schematic design, what is best for me? (How to deal with multi page schematics?) section multi page flat design.)
The question asked in the post you follow up is not automatically resolved by multi page options. The described problem is the fault of a missing feature in copy/paste. (Copy paste could offer options if it should reset references or not. Similar to how word processors ask if they should copy text only, text plus formatting, …)
The main usecase that can not be served right now is having multiple pages on any hierarchical level with local labels being confined to all these pages that are in the same level. I suspect this will the thing that will be implemented not some hack that means one has to choose between hierarchical or flat design.
See for example: https://bugs.launchpad.net/kicad/+bug/1688717