Because the websites want to serve ads to humans, upsell you, get you to sign up for their credit card too, so their implementation are highly obfuscated and dy

Because the websites want to serve ads to humans, upsell you, get you to sign up for their credit card too, so their implementation are highly obfuscated and dynamic. If they wanted to be easy to work with, they'd offer a simple API, or plain HTML form interface.