The device that you use for connecting to a WiFi network has a built-in antenna. Because of this, it's possible that it can't detect all the available connections in your zone due to weak signal strength. Also, some connections that you can't see might not be supported by your device. However, try to keep its driver up-to-date at all time. This will ensure that the device is running properly. All the available drivers can be downloaded from the official website.