99% of people want a messaging app that as many people as possible use. When the whole „WhatsApp user agreement“ scandal popped up I saw my opportunity to convince many of them to switch to Signal.
Quite a few did, but none of them really left WhatsApp. And since WhatsApp still had more people they know on it, over time most of them (me included) reverted back to just using WhatsApp.
RCS isn’t supported by every carrier, I wouldn’t even be able to reach all Android users I know. People with old Android smartphones don’t have RCS on their phones. And if I send media and they don’t have RCS it would get converted to MMS, which would cost me 0.40-0.90€ per MMS. MMS never took off in many European countries, thus it’s almost never included in the “free unlimited messages” carriers offer.
So it’s a complicated mess, a guessing game and a potential waste of money all rolled into one. Good luck getting people to use it.
As for ads, let’s not forget >Google had to actually turn off RCS for India< because spam messages became so rampant.
With stuff like this, it’s almost always one thing: Perception. There are multiple examples throughout iOS where UI elements are not centered or aligned the way you‘d think they should - purely because it would look „off“. It’s intentional.