Why are people obsessed with “breaking into” Apple’s walled garden? There are already secure cross platform messaging services like Signal or WhatsApp that has feature parity with iMessage. This is a solved problem that doesn’t need another solution.
Some people are finding themselves excluded from their social group because of platform choice - basically not being able to use iMessage (sometimes) means people don't want you in the group chat (because mixing iMessage and SMS messages makes a bad experience.)
It is incredibly difficult to get a social group to change messaging platforms, especially if that social group's shared interest isn't "using a good messaging platform"
The easiest solution is to conform to the existing messaging platform in the group. In the case of a bunch of iOS users, that might mean leaving Android for iOS. People don't want to do this (For a variety of reasons.) So being able to participate as a first-world-citizen of the platform has its appeal.
Holdover of them being obsessed with SMS for some reason too.
I remember having to pay 20c per SMS and 50c per MMS before IMs on phones became a thing. Wasn't hard for literally everyone to want to change to the first available client which for most people was WhatsApp, 2 years before iMessage was even released. Guess messaging was so cheap in the US that they didn't have a good enough reason to hop on the IM train for years.
Because its the Hacker ethos. People need to be able to modify any software to suit their requirements and not have to blindly follow the prescription of a company whose interests may not align with yours.
Most people in the US use iPhones. They also like to use the default messaging app, which most of the time is iMessage.
Some people like to use Android phones (privacy, cost, freedom), but still want to message their peers who use the Apple-only iMessage.
This is the best and most concise summary on the thread.
The equivalent would be if Microsoft, when they had the largest market share of email clients in the US in the late 1990s with Outlook Express (OE), decided to make it so OE-sent group rich text emails with attachments could only be received by other OE users, whereas non-OE users only received plain text emails with image thumbnails and downscaled video attachments. People would have lots of good reasons to use a different email client, like forthcoming Thunderbird, Gmail, or Apple Mail clients. But they'd find they couldn't communicate well with Microsoft OE users.
If Microsoft had made this change early enough and also made it so non-OE responses were color coded with a green background to indicate they are "lesser emails," we'd be in a world of Microsoft Outlook Express users would wonder why everyone doesn't just switch to Windows (the majority OS, at that moment) to make everyone's lives easier. And friends/family would exclude non-Windows users from an email thread as not to "degrade" the thread.
Communication via text with friends and family should be an open standard. Barring the availability of such a standard (e.g. RCS), at a minimum, the chat clients to communicate with friends and family should be x-platform (like Signal, Telegram, WhatsApp, and LINE all manage to be).
Ergo iMessage should, at least, have an Android app, even if such an app requires an Apple ID.