Why don't I have cellular option on my iPad?

No, there isn't. If you want cell capability directly from your iPad, you need to buy a new iPad. Or you can get an iPhone which would then (if set up to do so) allow you to make phone calls and send messages to and from the iPad as long as the iPhone is nearby.

Regards.

Because you bought a WiFi only iPad.

If you want cellular data, you have to buy an iPad that is WiFi/cellular.

Also note that even with a Cellular iPad, it is only for cellular data. You will not be able to make a phone call or send an SMS message from the iPad.

You can’t add it to a iPad but you could get a cellular hotspot from a cellular carrier or use the hotspot feature of your phone.