Lord Krishna is generally not worshipped as 'father'.He is worshippd as 'friend', 'master', 'lover', 'child' etc. Lord Shiva on the other hand, is worshipped mainly as father.
Sri Krishna told in Gita that He is the father of the world. Lord Shiva is known as the destroyer of the world often.
So why is Shiva worshipped as 'father' while Krishna is never?
I believe that both are the forms of the same Para-Brahman by the way and do not treat any of them as superior or inferior to the other.