Projects select proposals from students, not from their ideas list. The ideas list is a list for students of the kinds of things the project would like to see proposals for.
There's no guarantee that every idea will get proposals. Even then, you don't have to submit a proposal based on an idea from the list, and the organisations have a limited number of students they can accept, which is usually fewer than the number of ideas.
The short version is: the ideas are there to help you write a good proposal, but it's the proposal only that is judged.
Matt