Do you know how long it actually takes to fish up 200 fish (not counting multiples via sabiki rig)? That's about 4-6 hours, depending on bite rate. If you're telling me that you fish to fatigue on a regular basis without botting, I'm going to call you a liar. Considering things like Ahtapots/Grims, Black Sole/Dil, and Bastore Bream/Mercanbaligi average 650 to an NPC, that's a shitload of gil coming into the economy (which is more damaging than selling an item to another player, where the amount of currency in circulation stays the same).
Skilling up multiple accounts/characters is a big time investment for RMT, but they'll do it if it is the best time/gil/effort ratio. Remember how gardening used to be awesome for gil, and the RMTs all flocked to it? Remember how many legitimate players got banned because they had multiple gardening mules? SE has traditionally done a poor job at differentiating between RMT and the average player. I'd rather the caps stay as they are than risk more aggressive detection measures be put in place. It's better for the economy, and it's better for the players.
If anyone should be crying about their daily limit, it should be diggers. Digging is capped at 100 (without Blue Racing Silks), and pretty much everything that used to be worth digging (ie. ores, thanks Abyssea!) isn't anymore. It takes about an hour to dig up 100 items once you rank up enough to get a 1 second delay. On top of the 100 item limit, zones get dug up incredibly fast and the restock rate is much slower than it is for fishing. Did I mention how slowly you rank up due to the low digging cap?