Unfortunately our anti-trust laws were written in the 19th century, so they deal with very specific types of anti-competitive behavior. Modern tech firms basically grew up in an environment where the goal was to maintain the absolute minimal level of competition and user choice that stays within the law.
I'm not saying is impossible or something, but it's just way more effort than it was worth to me. E.g. so many iOS apps by default are set to use iCloud. All of my photos for years were in Google Photos. There is a Google Photos app for iOS, but it is in no way as seamless an experience as on a Pixel (e.g. camera integration). And I think a lot of people would say that if you get an iPhone but specifically avoid Apple's services like iCloud for photos so you can stay on Google's services, that defeats a huge part of the value of being on the iOS ecosystem in the first place.
For example, in Scandinavia the current marker leader on all platforms is Facebook Messenger, despite this also being one of the only markets where iOS is the dominant platform compared to Android. Further south on the continent, WhatsApp is the undisputed leader.
People have all of these apps, and it's my impression that using iMessage exclusively is extremely rare. Cross-platform support is a feature that impacts which app people use, and they are perfectly free to use a different messaging app.
That's less likely to happen to you in Scandinavia, perhaps since Puritans found it safer to set sail for New England than keep trying to evangelize Vikings.
Also, yes, everyone's perfectly free to use a different messaging app, and in different cohorts everyone does, which suggests it's not Apple's "walled garden" causing these difference.
* This has been true at various times, including times FB has said it isn't true. I did see the WhatsApp founder walk away from a billion dollars over various issues, and stopped using it then too.
https://www.news.com.au/technology/online/social/im-a-sellou...
https://about.fb.com/news/2023/12/default-end-to-end-encrypt...
The fact of the matter is that in the US, especially for specific socioeconomic groups, iOS is by far the dominant platform, and for many people since iMessage is the default, their definition of "texting" is simply iMessage. You state, "it's baffling to me that your friend group wouldn't simply switch to a messaging app with good group chat support" - except that completely ignores network effects, and many times I am literally the only person on Android. If I'm, say, going on a vacation with friends and literally 10 of them are on iOS and I'm the only one on Android, it's a losing battle to try to convince the other 9 to switch, especially since nearly all of their other contacts are on iOS/iMessage. A restaurant in Austin, TX, famous for their funny signs, even had a joke about it: https://www.instagram.com/p/CwLKeGRLieb
The reason the situation in Europe is different is primarily due to 2 factors:
1. iOS was never as dominant in the EU as the US
2. Perhaps more importantly, what is often forgotten is that in the EU and elsewhere about ~15 years ago, per-SMS rates from telecoms were egregiously expensive, while in the US by that time they were mostly unlimited with a flat monthly rate. So there was never a huge drive to get off SMS in the US (this is why WhatsApp first took off much faster outside the US than within it). In a pretty brilliant "Embrace/Extend/Extinguish" move, iMessage initially simply because the default SMS app on iPhone. Users never really "picked" any messaging app, they just continued to use the "texting app" that had always been on their phones.
I'm not a group messenger, and basically mute any group messages I'm a part of, so please excuse my ignorance. What's actually broken between iOS and Android with group messaging? Are Android-only group messages better? Will RCS improve this at all?
I'm an Android user, and a little less than a year ago I actually bought an iPhone, specifically due to Apple's iMessage lock-in (nearly all of my friends have iPhones, and the especially broken group messaging between iMessage and Android was the primary driver of my desire to get an iPhone).
Except the problem was that, after over a decade on Android, I had zero desire to switch over all of my data and apps over to iPhone. For better or worse the "Google ecosystem" is where all my stuff lives and I just didn't have a desire to spend a bunch of effort just to switch. I ended up giving the iPhone as a gift to an iOS-loving family member.
That's the thing about both iOS and Android platforms - I think you'll find anyone who has been in those platforms for more than a couple years will be extremely reluctant to switch just due to the effort. Our cell phones are often the center of our digital lives now: apps, headphones, watches, etc. The lock-in I think is more from that "ecosystem effect" than any amount of particular lock down.