Common sense? If Apple refuses to make obvious accessibility changes to drive customers to some alternative first-party product, that's probably going to get brought up during antitrust hearings.
iPhones are packed to the gills with accessibility features including for contrast, text size, bolding text, filters for the color blind, text to speech and color inversion.
It's not unreasonable for Apple to appreciate an aesthetic that is less accessible considering they provide the tools for users to customize the device for their needs.
The majority of people have no problem with the contrast of the Messages app, or at least it's never been a complaint that I've heard. That's not to say we shouldn't consider those who do have problems, but, again, there are options for those people.
That is in fact one of the accessibility settings. Increases contrast front the blue bubbles too, and color contrast between foreground and background colors system wide.
This might sound strange but most people with iPhones actually like how their phones look and behave. Personally I’m not the biggest fan of this era of UI design, but it’s silly to assume hostility on Apple’s part. Every year they announce even more accessibility features, and it makes sense to because they really want more people to actually be able to use the phones they sell.
You don't seem to have a great level of awareness of the world.
There are plenty of regulatory bodies, especially the EU, who have forced Apple to do things it doesn't want to.
They are making noise about interoperability of communications and rather than have the US (we don't have RCS over here, so it's meaningless for us) make rules that forces their hand in a manner that may not be how Apple want to do things, they get out ahead to reduce the power of the argument.
The fact that it's a shitty implementation is the feature.