Cannot mount ext4 filesystem with Raw Block

After initializing a ext4/ext2 filesystem with mkfs.ext4 cannot mount it:

After applying this:

nbd-rs init --size 100M raw "file:$(pwd)/raw.bin"
nbd-rs serve --export mydisk raw "file:$(pwd)/raw.bin"
sudo nbd-client -N mydisk localhost /dev/nbd1
sudo mkfs.ext4 /dev/nbd1

sudo mount /dev/nbd1 /mnt

hangs forever. (PS: It works fine with distributed/sharded)