we often tend to ask, why is so much of milk wasted on shivling? it would've been better if the milk was donated to the poor children than to waste it on shivling. many celebrities have made films on this topic. so, there are two aspects to answer the question put forth.
MYTHALOGICALY- Milk holds prominence in the puja of Mahashivratri. As per Hindu scriptures, Lord Shiva performed the 'tandav' on an auspicious night. It's believed that the dance depicts the cycle of creation and destruction of the universe. To calm him, he is offered soothing items like milk and honey.
As per this, people believe that milk calmed lord shiva and hence the milk is used.
Besides, shivlings are mostly placed near a well, river etc because the rishi muni had planned that the milk which will be offered to lord shiva, further can be used for donating it to the poor. It is true that after some attacks the places have been shifted but the real belief is this.
2 SCINTIFICALLY - Milk is said to be one of the best conductors of positive energies and when poured on the Shivling, the flow of energies begins to concentrate towards the lingam and the devotee becomes the received of the outflow for his close proximity.
The real question is if no one asks how much money is spent on the parents who raised us then why there is a question on people's belief on showering things like milk honey etc. why is there a question ?
if we see things in that way,
we light candles in church instead candles can be used to
light a poor man's house. if someone is willing to
shower their belief in god, why not?
As the offering of chadar at darga is done in the mosque, the chadar will be needed more by a man who is cold, isn't it?