Speaking for miniature naval wargames (my other hobby), the price goes up for two unavoidable reasons:
1) Few players. A sad reality of today gaming. Even those who publish their games without profit in mind need to keep the prices up to at least recoup their investment in time and effort.
2) Research (i.e. where time and effort go). Once you have a working rule set (already an achievement by itself) you have to research and translate into your rule set hundreds - if not thousands - of "platforms" (i.e. Ships, Subs and Airplanes for a naval wargame). A game like "Seekrieg V" (the virtual king of naval wargaming) offers, in its base package, a number of pre-compiled ship logs from various nations, plus some ready-to-play famous battles. Then, in its "GREAT BRITAIN 1880-1945" expansion alone, you find over 1,800 pre-compiled ship logs from the era - with each ship further detailed according to upgrades, refits etc. (so the USS Texas in 1920 uses a different log than the same ship in 1944). And whoe if you miss a single secondary AA battery on a torpedo boat.
So, it is apples vs. oranges. You can't really compare a detailed wargame with the base book of an RPG.