Earlier quoted context omitted.
I think you're misreading the above comment. He's pointing out that Apple considered green originally the best background color for texting, and then added their own protocol with a blue background. So it's not like they deliberately relegated SMS to green because they were certain blue was better; if they believed blue was superior, they'd have used it from the beginning.
Yes, and then Time Happened, and every other part of iOS was updated; including, by the way, THE GREEN BUBBLES, to make them less readable, I feel like I'm taking crazy pills and no one else remembers that they used to be a different shade of green, with black text, which has significantly more contrast [1]. Regardless, they could improve it at any time, yet its been like this for... a decade now? Cognizant Inaction…
As others point out, there are accessibility options for people who want more contrast (and which benefit users with trouble reading these outbound messages in far more useful places).