We fighter pilots are still around, just very few of us left though it seems. What I think is happening is new players are signing up, of course having 0 experience in this game and how to fly, and decide they just don't want to learn how to fight. Why should they when they can just out run you with their P51? And, as more new players are joining, the older vets of the game are retiring from the game or on long breaks.
The ratio of newer players to experienced players seems to be very lopsided towards newer players right now, and a lot of those newer players don't seem to be very willing to even try to learn some ACM.
The blame for the lack of fights in the MA could also be put on you scorepotatos. When someone new enters the game, they want to be the best. Ok, there's a scoring system in this game, so to be the best you have to be ranked #1 right? Guess who the people in the top 20 ranks are? Names of people who take Tempests or P51Ds to 20K over a furball and run when someone points their nose at them. Then the Tempy/Pony pilot has 4-6 friendlies come save him. Ok, not everyone with a good scores does this, but the new player sees the ones doing it land 7-10 kills and thinks "Oh, he's ranked #2 in fighters. That's how I have to fight get a good score!"
Some people have actually earned their score by just being that good! Most of the best pilots I have fought though have had rankings in the 1000-3000 because they only ever fly fighter mode, get 2-3 very well fought kills per sortie, and are not afraid to get into a cloud of red and mix things up.
I'm not saying "Oh, everyone in the MA is a wussy little dweeb, and this is how you have to play!" It's your $15 and you can play however you please. I'm just putting my thoughts out there as to why I think there has been a decline in actual fights in the MA.