Why voltage source is not included while using KVL?
It can't be 10−I1∙8Ω+I2∙4Ω=0 because, in this equation, you are trying to add voltage (I1∙8Ω+I2∙4Ω) and current (10A). Just like how you can't add 1m and 1 sec. They are in different units. You are not allowed to do that.