As zerker stated, it's one of Jagex's schemes to make money off.
So you're only choice would be "Be a member and pay every month, whether you play or not" or "Take a break, come back and pay almost x2 what you used to".
Most people would go with the first option, and it would get them a steady user base paying every month at least. And if they don't, they eventually will, and Jagex profits more.
This happened after the bot nuke. Tens of thousands of botting accounts are now idle or banned. And that is costing Jagex a fortune. I'm not sure why they did it, if they would end up losing a lot of money.