It would be considered a cash advance and the payee would pay huge fees. Credit card companies would never let this happen.
Many people would also use such a website for money laundering; turning stolen credit cards into cash.
People would abuse it for cashback/frequent flier miles, e.g. sending their “friend” (or themselves) money who then gives it back… rinse and repeat. This is against all T&C of any card, and again would be a cash advance.
If you want to send cash, you need to send it from your bank account, or using actual cash. There is a reason it’s “crazy expensive” and to put it simply a credit card is not your cash to send.