It’s common to receive a mail from some service that they’re changing the terms and conditions of their service (internet provider, gmail, etc.) These changes are unilateral and can be about anything, from their privacy policy to the money they intend to charge me.
Why can’t I unilaterally send them a mail and say, I am changing the terms of my patronage and will now insert my new policy (pay only xx amount, or demand a mint Chico chip ice cream every Tuesday)?
You want to blame Singer Sewing Machine company for this. They’re the ones in the 1850s that came up with the idea of pre-made non-negotiable contracts. Before this, every single contract had to have lawyers adding and removing terms until both sides agreed to it. I know today’s version sucks, but the alternative could be worse.
Imagine having to bring (and pay!) your lawyer to a car dealership to buy a car or even sign up for Netflix. Imagine how much more expensive the goods and services would cost you because of the army of lawyers needed to negotiate contracts for every single consumer.