Why most of the motor with blades rotate anti clockwise when viewed from the front?

This is the same idea as the direction of rotation of aceiling fanor a box fan. Motor fans work by pulling air in from one direction, and pushing it out the other direction. Which side is the "in" side, and which is the "out" side, is determined by the direction of rotation of the blades and by the direction of the pitch of the blades. Most fans have their blades pitched so as to follow a "right-hand rule." If you stand in front of the fan with the fan blowing towards you, hold your right hand in front of you, and curl your fingers so they curl in same direction as the rotation of the blades, your thumb will be pointing towards you. There is nothing physically inherent about this direction: if you reverse the pitch of the blades, you will reverse the airflow without reversing the rotation of the fan. For most fans, it's just a convention that they do this.

There is one situation where inherent physical considerations affect the choice, asOlin Lathropalludes to in a comment. Motor fans can be quite heavy and can rotate quite fast. When they do, they produce a huge angular momentum, which can make steering difficult. Using two fans pitched in opposite directions allows you to have both fans push air the same direction, and rotate in opposite directions. You then have zero or very little net angular momentum, and easier steering.