>>103105168
I was going to type out a long response about the persistence of progression and constantly having new goals to make and reach even without the game having to seasonally update with new content but >>103105701 explained it pretty well.
Even the very first areas of runescape ever added to the game still serve a purpose almost 25 years later and there are very few pieces of content that are truly abandoned aside from some random minigames like the rat pits