Personally, I don't get it. I communicate with my friends who use iPhones all the time with my Android devices and never have a problem. But then, I don't tend to depend on every feature known to messaging.
But, on a certain level, I do understand it. When I'm communicating with other friends who use Android (as long as they have RCS enabled), I get all the bells and whistles (read receipts, group chats, rich media sharing, etc.) And RCS isn't limited to Android; the protocol is available to Apple…they're just adapting it next year.
Beeper (the company) first came into being in 2021, and they had a rather lofty goal…bring everyone's chat applications together within a single UI. That goal would allow both Android and iOS users to experience the same features, without missing a beat.
Finally, Beeper has made this dream a reality, with its new Beeper Mini app. The app (launched today) makes it possible for Android users to chat with iOS users (enjoying all the features they want), without having to first sign in with an Apple ID (which many Android users don't even have).
According to the Beeper Mini description, the app brings the blue bubbles to Android, your number shows up in blue, and all chats are secured with end-to-end encryption. Understand, however, that Apple is famous for "breaking things" to prevent third parties from accessing its features. But given Apple's intention of adopting RCS, I believe the chances of this happening to Beeper Mini are slim.