As part of the FSE Outreach Program's Build a Block Theme exploration, the following was brought up:

How the heck do I delete pre existing templates? Such as Two Page templates Page (Large Header) and Page (No Separators). As well as the extra Single Post (No Seperators) template.

Right now, when you install a block theme, there's no option to delete or disable current templates. You can only delete custom templates or reset customizations to current ones. This is because template files that are bundled with your theme are not stored in the database. For folks building block themes or even switching between block themes with a desire to mix and match, this becomes a more important flow to unlock. This inherently relates to #25071 in that it's another use case around it in many ways afaik.