Because it has been proven to be RS gold effective. It is impossible to keep up with the speed of this game. Not just from a gaming perspective but also from a commercial standpoint. Jagex has to earn profits, pay taxes, and also pay its employees. If they didn't keep runescape on par with competition it could quickly be a victim of.
The ability to adapt and progress is essential to everything in life, but in the age of technology it is even more important. While you could buy OSRS gold argue that humans have become the dominant species due to changes in their environment, this is not the case.