TLDR; the "Could Not" error can be attributed to either outdated content or the removal of the file by its creator, both of which hinder your ability to access it.

The "Could Not" error may arise due to a couple of key factors.

Firstly, the content might be significantly outdated. This means that the file you are attempting to access is not compatible with the latest version of Minecraft, which prevents you from downloading it. The game continuously evolves, and older files may not meet the current standards or requirements.

Secondly, there is a possibility that the content has been removed entirely. This could occur if the original creator decided to take down the file for various reasons, such as copyright issues or personal preferences. In such cases, you will not be able to find or download the content anymore, as it is no longer available to the public.