Why is WhatsApp not supported on my iPad 10th generation?

The WhatApp developers have not released an App compatible with iPad - the App being currently limited to iPhone.

Whilst the App is not available for iPad - you should be able to access the service using a web browser:

https://web.whatsapp.com/

SBI-1998 wrote:

WhatsApp not supporting iPad 10th generation but why

That's something you'd need to ask the developers of WhatsApp.