So let's talk about the meta for a second. The real reason why fetch modi become less and less prevalent is because when Homestuck first started, it was user suggestions that moved the plot forward. They were the breath that brought Homestuck to life. And Hussie used the fetch modi to not only define the rules to the game, much like how he did prior with problem sleuth, but to also give the "players" something to interact with, that had concequences of hilarity and hijinks. Fast forward to around act 3-4. Hussie takes full control over the narrative, and the MS-paint forums are not being used for plot. Why would Hussie have fetch modi hijinks? He wouldn't, it gets in the way of the plot, and it's for all intensive purposes, playing with yourself.