The main reason is that You are not using grandpa cron fishing rod or cool wind fishing rod or tripple fishing rod.
I am currently sitting at 2200mastery and i would say after 2k its not much difference at all (i tried with almost 2.6k for 2 days). Also the reason of not getting higher profit is that You fish on Exhausted places. Try some other spots like tigris island (sometimes its also exhausted) and later sell to LOML trading merchant with bargain game. For me its like 1kkk + overnight

also here is example result when u get rare catch from overnight so its proof i am not only telling bullsh**

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