Why can I not send sms text messages on my iPad when my iphone is turned off? I'm also connected to Wi-Fi?

Why can I not send sms text messages on my iPad when my iphone is turned off? I'm also connected to Wi-Fi?

Your iPad is sending SMS text messages based on its connectivity to the iPhone. SMS doesn't use Wi-Fi, it uses the cellular/mobile network, and if your iPhone is off then the iPad can't go through it to send SMS. IMessage would work over Wi-Fi.