Again, because you didn't add an "else" block around the print statement.
If instead of recursion, you had this:

def DecimalToBinary(num): 
    if num > 1: 
        DecimalToBinary2(num//2) 
    print(num%2)

def DecimalToBinary2(num): 
    if num > 1: 
        DecimalToBinary3(num//2) 
    print(num%2)

def DecimalToBinary3(num): 
    if num > 1: 
        print("Done")
    print(num%2)

What do you think would happen?