Why the Nginx config in Laravel Octane documentation use close instead of keepalive?

I found that the Nginx config in Laravel Octane official documentation set connection close instead of keepalive when proxy passing to Octane listening port. Could anyone tell me why?

The config is as follows:

map $http_upgrade $connection_upgrade {
    default upgrade;
    ''      close;
}
 
server {
    listen 80;
    listen [::]:80;
    server_name domain.com;
    server_tokens off;
    root /home/forge/domain.com/public;
 
    index index.php;
 
    charset utf-8;
 
    location /index.php {
        try_files /not_exists @octane;
    }
 
    location / {
        try_files $uri $uri/ @octane;
    }
 
    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt  { access_log off; log_not_found off; }
 
    access_log off;
    error_log  /var/log/nginx/domain.com-error.log error;
 
    error_page 404 /index.php;
 
    location @octane {
        set $suffix "";
 
        if ($uri = /index.php) {
            set $suffix ?$query_string;
        }
 
        proxy_http_version 1.1;
        proxy_set_header Host $http_host;
        proxy_set_header Scheme $scheme;
        proxy_set_header SERVER_PORT $server_port;
        proxy_set_header REMOTE_ADDR $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;
 
        proxy_pass http://127.0.0.1:8000$suffix;
    }
}