What's up with the strange privacy verbiage?

Why do privacy tools use verbiage like "tell websites not to sell or share data" and "send do not track requests" instead of just blocking websites from accessing my data? I've seen similar language used by many companies (Apple, Google, etc.) and I've also seen that many websites don't respect such requests. I'm pretty new to privacy and I'd appreciate a brief rundown on how this stuff works.

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