Crafting is different because it doesn't bring new resources into the game (apart from gil from NPCing items), you're simply using materials that already exist.
No sane gatherer wants there to be a situation where a player can bring unlimited mats into the game because the prices of everything you gather would hit rock bottom within days. They would be worth barely more than the price you get from an NPC. Look what happened to zinc, silver and obsidian ores during the period when everyone was soloing doblyns to rank up. Those ores because almost worthless.
As a crafter you may feel happy paying 500 gil per ore, but then why bother playing gathering classes at all? Only the rank 50s would benefit, because they won't need to gather again until new mats are added and then they can charge you 100k per darksteel ore while your MIN is sat at 1 because you had no motivation to rank it up due to everything being worthless.