Let me explain this in basic language when you are planning to get married just looking at picture of your would be bride or groom you cannot finalize your decision, as you would like to understand the nature of the person, likes, dislikes, habits, compatibility and so on . The same thing implies to your Idea.
Idea is thought which you feel as individual its good and best in market, in more simple language it’s like your kid is the best and brilliant but it’s the teacher in school which lets you know the truth.
Let’s analyse this in business language, Idea which cannot generate revenue is not an idea but its just a thought. The same thing applies to your idea also if its not generate revenue how will investor invest his money, don’t have thinking that there are people with lot of money in surplus remember though they have in surplus doesn’t mean they will give it, also understand for having money in surplus how much they have worked to earn and have funds in surplus
So having idea is not good enough to raise funds, yes I do agree there can be exceptions.