I'm out of the loop (I tried 2007scape but don't play it enough to be in the know). Is it because some other faster way of leveling Runecrafting has become available?
I suspect Law crafting (with runners) would still be more XP per hour, but I think the player dynamics are quite different nowadays. You used to spend a lot of time at the start trying out various things that are no longer "efficient" (another thing I remember doing was mining rune essence—I didn't do that at all in OSRS). I think it's because of a combination of things, like the age of players (younger people might not be as good at strategising), visibility through social media (eg, Twitch/Reddit) about how to play the game "properly", and modern updates that make some of the tedious tasks unnecessary (in Ironman, I think I got my rune essence from newer PvM and the "Temple Trekking" minigame). For all of these reasons, you don't end up with people that would be willing to queue to trade their time for someone else's runecrafting experience and a couple of Law runes.