First of all, because of the war crisis, Nanjing has been unable to make the Southern Song Dynasty stand on its feet. The shame of Jingkang occurred because the nomads from the army were ferocious, and Song Gaozong's brother and most members of the royal family were captured, while Zhao Gou was able to escape successfully because the nomads from the army denied him. Zhao Gou didn't come into contact with the core politics before because he was disliked by his father, and Zhao Gou didn't have the ability to organize forces against the nomads from Nanjing, so he finally gave up Nanjing.
Secondly, due to the sudden disaster in Nanking, the ministers of Zhao Gou and North Korea at that time fell into chaos. In that case, the first thought is to escape and save their lives. Because Nanking is too close to Xu Jinguo's ruling area, it is impossible for Zhao Gou to resist the attack of Nomads from the Golden Army. Finally, I gave up Nanjing and made Hangzhou my capital.
Moreover, Hangzhou's economy is very developed. After the Anshi Rebellion in the Tang Dynasty, the economic center of China began to shift from the north to the south, so at that time, Hangzhou basically became the most economically developed area in the south, so it was beneficial for Zhao Gou to make its capital here.
Finally, Hangzhou has a well-developed waterway and is one of the three major ports in the Song Dynasty. Zhao Gou, who suffered from the humiliation of Jingkang, felt very sorry for his life, so Zhao Gou had long thought about his retreat. If he can't resist the nomads from the river, and the nomads from the river are not familiar with the water, then he can escape from the water smoothly.