Because while it is scouting for carriers almost everybody else who is participating in the scenario is sitting in the tower twiddling their thumbs. Further, should it fail to find the CV and instead be shot down by some roving A6M2, where does the scenario go from there?
What are the Japanese supposed to be using to scout for the American CVs? If they are using a B5N or D3A, does that not give the Japanese a much better chance to find the Americans first due to their higher speeds?
Basically scenarios right now - are limited to 1 sector for carriers, because we have no scout crafts, For example "your enemy carrier will be in sector 1.1.x ". Instead it could be put on a historical course while scout crafts have to span out and search for it. Sure the B5N would be faster unless the Pete is added to the game, that just means the Japanese get to meet American F4F's and SBD's quicker. The Raid will launch in the general direction of the fleet, as did midway.
Secondly if there is any Clouds in the game, it would certainly hide a PBY, which flew no higher then 6k when spotting for carriers. Sure you can bring a few A6m's down to the deck, that just causes a Midway effect and you lose a carrier. Even if you put 1-2 A6ms on the deck, what chance it will find the PBY? Also how could the PBY not already Report back the location of the enemy fighters? Surely A6m's didn't fly from land base during Midway/Moresby/Coral Sea, so clearly if you run into an A6m you report it and the Strike group can be sent on their way.
It brings a higher level of strategy to the game then "Btw your strike group launches from C1 to attack enemy carrier in sector 1.1.x - when you could put the carrier on a course and make people find it - adding a level of uncertainty.
Sure it wouldn't be flown in the Main Arena much, neither would the Emily - difference over 3,000 PBY's were built while barely over 90 Emilys were built.