Why was this visual proof missed for 400 years? (Fermat's two squaretheorem)

https://www.youtube.com/watch?v=DjI1NICfjOk
Channel: Mathologer
Times watched: 3
Watch Times
Date Before
2025-03-08 15:18 1 year, 8 months
2025-03-07 22:21 1 year, 8 months
2023-12-08 11:35 2 years, 11 months