Why Don't You Add Cards? You Know Those Credit, Debit Cards

First, you explain your suggestion in the body of the message. https://en.numista.com/help/forum-policy-77.html

Second, Numista is not s shop. We don't need credit/debit cards here. https://en.numista.com/help/can-i-buy-or-sell-on-numista-7.html

He wants to add credit cards as type of collectible object, like banknotes, checks, etc. 

I would suggest if you want to collect credit cards use Colnect.

I guess that Credit Cards and the like would find a place in Exonumia. However, they might also be regarded as ineligible, as are stamps - too different a collectible to be included.

Credit and debit cards, telephone cards, gift cards, etc. are out of scope.

The more you extend the scope of catalogue, the less detailed, meaningful and exhaustive it becomes.
The current scope is already very large, accepting all kinds of coins, banknotes and exonumia from the entire world and from all periods (see details here). Designing fields and features that are meaningful for such a wide variety of objects and aiming at exhaustivity is already challenging enough. Therefore I don't plan to increase the scope.