It is my understanding that a lot of thought and care is put into the design language and appearance of applications and frameworks. However the same level of consideration is not usually afforded to skins and themes, which are often released an never updated again. This can cause usability issues and sometimes even breakages. Of course, people are free to do as they please with their computers.
To add, you could have looked this up before posting a hostile comment on a relative newcomer's post. This is how linux communities develop reputation of being exclusive & unfriendly.
SMS and MMS are not very secure however. RCS is technically an open standard. it's mostly controlled by Google at the moment, but hopefully that will change as Apple enters the game this year.
I remember trying to play the original when it came out and not having a great time.