Pinterest: you cannot put a Pinterest link in a pin??

Hi all,

I created a board with product pins inside, and I'd like to post cover pins in group boards that link back to that board I created, not to content outside Pinterest. However the system doesn't let me put a Pinterest link in a pin:
"!To save an idea you find on Pinterest, use the Save button you find on each Pin".

Why could a pin only link to content outside Pinterest, and not to a board?

Thanks for your help