ls doesn't have the version sort option so since you're aliasing a piped command to sort you'd be passing any additional commands to sort

So

ls -r

Would actually be

/bin/ls | /bin/sort -V -r

You could overcome this with xargs but it's just definitely a bad idea in general to alias a standard command piped into another command. Will cause headaches.

Where as something like

ls="/bin/ls -r"

Just defaults ls to a reverse sort and you can still safely add additional args.