The real issue is that Apple has to have some fallback protocol for texting with non-iMessage devices, but refusing to upgrade the fallback protocol beyond SMS/MMS makes the texting experience worse for everyone, as described in the article.
(To avoid additional red herrings. No one is thinking here about opening up iMessage itself to non-Apple clients, just upgrading the fallback option. Also, I can't speak for everyone, but among the non-terminally-online Gen Xer and late-Millennial Americans I know, "texting" means using the built-in app on your phone. Switching to another app is a relationship step. Many of them are blithely unaware that they can't "just" text a photo or video to me or other Android users, nor that I can't just sign out of a group chat when I feel like it.)