It's simply the result of chasing performance with aesthetics being a secondary concern. I think a lot of comparisons of F3A planes to Formula 1 race cars are valid including appearance. F1 cars are ugly compared to a Lamborghini or Bentley, but you can't argue with the performance. Machines that perform well have their own beauty though. There is a difficult to define beauty to the F3A planes that fly well. It's like the human eye instinctively knows what works.