I agree with
terrynguyen121988’s comparison with exam. We study for so long but the exam is a different challenge.
I can only observe as a layman, but from what I’ve seen:
Training hard could be a routine and needed to hone skills, build their form and endurance. But the actual tournament is different in pressure, intensity, focus, mentality, opponent (most of the time), situation (hall, shuttle, drift), etc. And athletes are also still training, doing physical exercises, go to gym, practice on different halls during the tournament.
Different playing conditions require different approach, adaptation and adjustment, which is usually different with their training situation. Players who are used to fast halls might find slower hall challenging and vice versa. And slower halls consume more energy. Plus traveling to multiple countries, different climate and weather, multiple hotels, packing/moving in-out/transportations, dealing with jetlag, food, injuries, being fed up, disappointment and many other challenges. All of those put a lot of strain on bodies and minds.
And these past few months, after +1 year of no international tournament, suddenly the schedules are packed. Major tournaments mixed with regular tour with little gap. The greater the result (SF and higher) means more match and less resting time. Training hard is important but so is recovery time.
Multiple players already admitted about them being tired, on top of my head: Ginting, Momota, Yuta-Arisa, Minions, Antonsen, Sapsiree. It’s not a coincidence that top athletes that already train really hard are still troubled with difficulties. For example, multiple Top MS (e.g. Jojo, Ginting, Momota, LZJ) are now dealing with injuries, fatigue and pain on their body parts.