Fabby, if you increase the amount of fish people can catch in a day it would indirectly increase the number of bots. It would also squash the amount of profits that crafters are able to make, namely cooks.
RMT fish to make real money. When you limit the amount of fish they can catch, you also limit their profits and their numbers go down. Go to youtube and search for "Batallia fish bots" and click the 1 minute video with the title in japanese. A good look at how it used to be before they added patrols and limited the number of fish and items you could catch.
Now think about those hundreds of fishermen going all day long, stopping only for a few moments to trade stacks of fish to a runner who would go place them on auction or vendor the trash. I'm not sure if you do, but many fishermen supplement their gil income with cooking. Thousands of fish flooding the market has a direct impact on profits of other crafters or even you if you cook as well.
In the end I agree that it sucks that you are limited. Personally I couldn't fish for 3 hours a day, but if that's what floats your boat then you still have that opportunity. Sure you have to spend an extra dollar or two, but that is hardly worth being upset over.
If you are going to criticize, you should at least come up with a better suggestion. The limits may not seem fair, but the reason for those limits is obvious and for the most part, effective. Come up with a better idea and you might have something here.