Because capturing ships is soooooo easy in troop VS troop combat that its just a waste of time, and rather boring after the first few bouts. How so? Just walk backwards. Walk backwards, casually drifting in a circle. The enemy will virtually always miss, while you can take brief moments to stop, turn, shoot, then continue moving. Eventually you'll take down all the enemies. I've done this with as many as 5 against just me. So I just play in easy mode because troop combat is too easy.
By the way, whats that uber ship with the super laser that destroys everything in site called? I just captured that for the first time on my fourth game, but I never got its name... It sure makes getting rich easier. After I took out the space station, I just kept attacking earth until I was so stinking rich I didn't have anything to do with my money... Last I checked, I had 50k and nothing to buy. And about 2k fuel too... Its too bad there isn't more to do in this game