Just an update for whoever ends up on this comment.
This feature works as long as your venv that uv creates and the uv cache (in user home directory, or anywhere else that is configured to keep the cache folder) are both on the same filesystem.
The drive where the venv was created was NTFS and the user home directory where uv cache exists was ext4 file system.
Therefore the caching didn't work and a warning was shown by uv hinting to the problem.
This feature works as long as your venv that uv creates and the uv cache (in user home directory, or anywhere else that is configured to keep the cache folder) are both on the same filesystem.
The drive where the venv was created was NTFS and the user home directory where uv cache exists was ext4 file system.
Therefore the caching didn't work and a warning was shown by uv hinting to the problem.