>Americans hate the iMessage experience
No. They love the iMessage experience and iMessage inertia means that people without iPhones have to negotiate to get people to use something else. It's not even necessarily malicious or obvious, but it does happen. I was a little hurt when I realized I had been left out of certain group communications that were happening over iMessage when I didn't have an iPhone.
>but for some reason they refuse to use any of the numerous free alternatives?
I guess you could say that, but it's more that the inertia pulls them back to iMessage. I'd try to get people to use Signal/Telegram/Whatsapp/Messenger and at some point, they'd stop checking those apps and I'd have to send them a regular SMS. I was the only person they were checking the app for, so any lapse in our communication could result in forgetting to check the app (and even having it get automatically offloaded).
It's also kind of like being the only vegan in a group of meat eaters. They just get invited to less dinner parties when people don't want to go somewhere that accommodates the vegan's diet. That creates a social rift even if it's not obvious.