Why doesn't rsync peform delta transfer when copying from a disk to cloud storage?

I believe the rsync manual says that incremental file transfers are performed when transferring files across file systems. However rsync's output below shows that delta-transmission is disabled when I'm transferring files from a disk to a cloud file storage mounted on a directory. Why isn't delta-transmission enabled for this filesystem boundary crossing transfer and how can it be forced?

$ tail -f out.log
[sender] expand file_list pointer array to 1024 bytes, did move
[sender] hiding directory home/user/cloudDrive because of pattern cloudDrive/
[sender] expand file_list pointer array to 1024 bytes, did not move
[sender] expand file_list pointer array to 1024 bytes, did not move
[sender] expand file_list pointer array to 1024 bytes, did not move
[sender] expand file_list pointer array to 1024 bytes, did not move
[sender] expand file_list pointer array to 1024 bytes, did not move
[sender] expand file_list pointer array to 1024 bytes, did not move
created directory /home/user/cloudDrive/folder/2024-09-27T00:06:05+02:00
delta-transmission disabled for local transfer or --whole-file