Impressive to the rest of us, but I can see why to them it's disappointing, if they've been aiming at gold, and if they were expected to get it.
Each athlete will have their own goals, whether it's gold, or any medal, or top 10, or whatever. If they beat that, great. If they don't, then of course they will be disappointed and re-living every possible mistake - especially if they are interviewed right afterwards.
It's the same in any field, academic, music, sports etc. If you are capable of, and expecting, to get 100% at something, and you miss a few points, you will of course be thinking about those marks and what you could have done - it's how you get to the highest levels, by thinking always about those little details, let nothing escape, work out how you could have picked up marks/points/goals etc. You can't then just forget all that because it's the Olympics, and think 'oh fab, silver is great now' or whatever, if you were in contention for gold. Or be happy with 11th, if you were hoping for top-10, etc. You have to focus on the mistakes if you want to improve another time, and it's really frustrating to have people always saying 'oh be proud of what you've done, this is a great mark/score/place', when to you at the point, it's not. Or even if you ARE proud of it, you are still interested in and want to talk about what went wrong!! I think with the passage of time, that attitude changes, and people are proud of what they achieved over a career, but at the time, focusing on mistakes is both natural and necessary for improvement.
And also, it must be so awkward being interviewed and trying to figure out what to say, and how to come across to the public, etc, how not to seem arrogant, etc, and it could be easy to come across the wrong way.