Ever had a great idea and pitched it to a gatekeeper only to hear the words, "We do that already?" Or, in another form, "We know that already." Pretty demotivating, isn't it? You stop pursuing the idea, only to learn later that your idea hasn't been investigated, no one is working on it, or someone started working on it after you made your pitch.
The gatekeeper has one or more reasons for their response. One, they may simply not understand what you are saying, and mistake your idea for an unrelated idea. Sometimes the gatekeeper may be making a snap decision about your standing or ability to pursue the idea. At worst, the gatekeeper is thinking, "That's a pretty good idea. I need to take this back to one of my people and have them look into it."
Keep in mind that responses to your ideas are just data that you should collect and analyze more fully. A response of "We're on that already" should be met with polite skepticism. Keep generating those ideas, and pitch them to a lot of people, and triangulate the responses. You may find that your gatekeepers don't know as much as they claim.