This is the first Gran Turismo game I've played (and its simply fantastic!) but I think jdc is right about making it relatively easy offline, so it appeals to more people. It needs to be easier, so more people can do well at it.
We all know you don't make enough money during the A-spec races, its too time consuming to let your b-spec grind for you. So the seasonal's are there to really open up the game by letting you win, and get the XP/money you need to get what you want out of the game.
adeadsnipermatt made an excelent point too. The real challenge to win races in this game, is to play online. There are a lot of really good drivers out there, and you won't see them if you don't play online.
Playing online will also help improve your skills. Here's a TIP for all those out there that crash and burn on the first corner. Don't try to win (cause you never will if you don't drive properly), just try to keep up!
Practice in the seasonals too, since the AI pretty much gives up on life if you bump into them. Try to pass them without hitting them.