Q: Hi! Why I'm not able to pair my iPhone with my iPad through Bluetooth? Tks

iOS: Understanding Personal Hotspot

http://support.apple.com/kb/HT4517

Use Bluetooth to tether your iPhone, iPod touch, or iPad

http://www.macworld.com/article/1159258/bluetooth_tethering.html

How to Connect an iPad to an iPhone Via Bluetooth Tethering

http://techtips.salon.com/connect-ipad-iphone-via-bluetooth-tethering-25472.html

 Cheers, Tom

Because there is no reason to do so since data sharing over Bluetooth is not supported.

What are you trying to do?