Personally I don't see the big problem here. You get so many courses and races for free, does it really matter who you have unlocked and what carts you have overall? Considering this isn't a game used for tournaments and obtaining real world prizes and is made to play for a bit and then move on with your day, why is it a big deal that Nintendo charges people to unlock stuff like this? As others have said, you can still possibly unlock these items by just playing. Are people so concerned about a scoring system they share with their friends, that has no impact on anything, that you feel you're forced to buy these characters and carts?
I'm still using Toadette, her standard car and glider that was originally unlocked and consistently get 1st place in races and get new courses without issues. Is the problem that most people here, who are complaining aren't able to get over 10th place and races aren't unlocking for them? I'm generally curious as to why this is such a big deal for a company to make money on a product they produced.