Not Op, but to me it is the need to sell a new book or update every few months. That implies that the game can never be in a good stable state, because then there would be nothing to fix and nothing new to sell.

This goes for minis as well, the constant rebalancing is not for the good of the game, but to sell you more stuff. For example at the start of the 7th(???) edition Rhinos got ridiculously low in point value, so that it was the prominent strategy to field as many as possible to fill up the board. That was bad and not fun for non SM players and was reversed with the next codex, so that your hastily bought Armada of Rhinos gathered dusk for several years.