1. This is the 'gatekeeper' problem. You have a handful of people deciding if you're making "what people want". They can't possibly know what all people want. JK Rowling got rejected by, what, 20 publishers? They can't know. They can only do their best. The 'gatekeeper' problem also means you get idiosyncrasies, such as (essentially) a ban on single founders, etc.
2. Some ideas are easy to pitch, others nearly impossible. Take this year's Best Film Oscar winner, "Slumdog Millionaire", and try to pitch the plot in a way that's not ludicrous. You won't succeed. But take any cheesy, crappy B-flick and you can perfectly summarize it and even make it sound good. Now, I'm not saying there's a correlation between a good idea and difficulty in pitching it. (Ok, but I will say there's a clear correlation between mediocre ideas and ease of pitch.) So if you didn't get accepted, your idea either isn't very good or it's great.