Years ago (and yes, I am a Runescape vet), the whole world was free. The free world we see was the entire world. Runescape was constantly expanding. People were excited. Servers were spawning everywhere. There use to be around 10 servers. Look at it now.
Jagex wanted to keep expanding; however, they could not afford bandwidth. This is where Jagex had a solution.
They planned to raise about 2000 dollars via Pay Pay. This meant that, if each player had sent in a dollar, they would have got enough money to expand.
But they made about 600 dollars in one month; they were discouraged. They decided to therefore make all future expansions priced. This is how members started
It the classic Runescaper's faults (including my own); this is why it isn't free.