這個問題在nginx文檔中可以找到原因

If a server is the only server for a listen port, then nginx will not test server names at all (and will not build the hash tables for the listen port). However, there is one exception. If a server name is a regular expression with captures, then nginx has to execute the expression to get the captures.

也就是說，如果某個端口下只有一個server_name的時候，所有訪問該端口的請求，不管server_name是什么，都會由該server塊處理。

請看 Server Names。