Because I have no issue with sms. Is there some lingering bugs with SMS im not aware of?
The saying doesnt go “if it aint broke, fix it”
Well, arguably the most important aspect of RCS is security. SMS is entirely unencrypted, whereas RCS supports E2E encryption. There's also improved photo quality, bigger attachments, longer messages, etc.
It's not as if you lose stability or anything with it. It only adds enhancements.