"Stop using the product" works for coffee, where if you don't like it you can try an alternative. But with the cash cows of mega corps you often have few alternatives and it's intentionally difficult to switch.
I don't understand why some are wary of government regulations, but have no qualms about being controlled by major corporations where you don't even have a vote.
I used to use iMessage every day. It was my primary mode of communication for 10-ish years. I bought iPhones as gifts for others who didn't have them, just so we could iMessage.
Today, I never use iMessage. I'm not logged in to it on any devices. A big part of this was Apple backdooring the end-to-end cryptography (with full plaintext message history and key escrow via iCloud Backup, which is not e2e encrypted, and on by default for all users) which makes it way less secure.
Turns out that iMessage is optional. All of the other forms of communication that existed before and after it are still available to you as options. There's no law or any requirement anywhere that you use it.
"Lock-in" is colloquial: you're free to leave at any time. I was, and I did. Anyone can.
