Why is it hard to accept feedback from people junior to me?

You can hear a peer or a boss, but when it comes from someone below you, something in you discounts it. The direction of the feedback, not its truth, decides how much weight you give it. That is a filter, and it is costing you good information. A junior person often sees things you cannot. They are closer to the work, newer to the assumptions everyone else stopped questioning. Rank does not decide accuracy. The most useful correction can come from the least senior voice in the room. The next time someone junior offers a view, treat it as if a person you respect had said it. Ask one real question about it. You are not lowering yourself. You are getting smarter by widening where you will listen.