I read the rule and thats it but I would like a reason why the first naval unit has to be turned facedown and in adg's wif same thing when naval combat starts. A rule is a rule I understand that but can anyone here explain to me why that rule is in effect, what is or was the thinking here?
First in case of confusion in view of the title of your post - flipping a naval unit is not the same as aborting it.
In WiF, flipping units is akin to using their capacity to act. For land units it is more a case of being disorganized by combat or moving in difficult terrain/weather. But for air and naval units, if they get used for something during a turn such as supporting an attack, ground striking, invading, or shore bombardment - or in this case initiating a serach for the enemy, they are "used" for the turn, unless they can be re-organized.
It's true that the mechanic works to prevent a player from searching impulse after impulse with just one unit in the sea zone.
If a naval unit is flipped already, there are times you'd welcome getting it aborted (either voluntarily or by combat) so that it can go somewhere that it can be re-organized - and then you may be able to use it again the same turn.