You're forgetting the fact that everyone has different tastes. You may think that certain cars are 'pointless' but other people may think they're fantastic. I personally prefer to drive 'normal' Honda's and Nissan's to their limits and I find driving track cars which grip like they're on-rails to be mostly boring. Everyone has different preferences and therefore Gran Turismo's car list won't ever fully satisfy every single person who plays it.
Also, I've found the overwhelming majority of people in the GT5 part of this forum are completely missing the point of the Gran Turismo series. It's not about only track cars and race cars, it's also about normal cars that you'd see driving around the streets in real-life, such as Honda Civic's, Vauxhall Vectra's, etc.