Because the old man and the seagulls had a deep bond with each other and wanted to stay with the old man for a little while longer, not wanting to be separated from him
This was something that no one could have imagined. The seagulls may have thought that the old man had come to feed them again when they first started to "suddenly fly in", and since the old man had not come for many days, they could not wait for the old man to call out their names, so they "suddenly flew in". However, they soon realized that something was wrong, so they circled around the statue, "flying and circling" and "chirping". They must have realized that the old man, with whom they had been living every day for more than ten years, was not the same as usual today. They call out to the old man with their chirps.
Seagulls are like people, they have human emotions. After the rapid flight, the seagulls "have landed", "actually in the old man statue before and after the two lines", they are so serious and quiet, perhaps they know that the old man will never come back, so they silently "stand in silence! They were so serious and quiet, perhaps they knew that the old man would never come again, so they silently "stood in silence" as if they were keeping watch for the old man. I believe that anyone would be touched by such a scene.
Seagulls are also like people, they have the same emotions as people. After the rapid flight, the seagulls "have landed", "actually in the old man statue before and after the two lines", they are so serious and quiet, perhaps they know that the old man will never come back, so they silently "stand in silence! They were so serious and quiet, perhaps they knew that the old man would never come again, so they silently "stood in silence" as if they were keeping watch for the old man. Such a scene, I believe that no matter who will be moved.