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Who decided what the existing minimum fees are? Greenspan?
Are there minimum fees? If so, what are they/who/ how were they implemented?
If the miners choose to mine everything, obviously there is a bypass to that.
Implementation is part devs - of any coin, not just btc - (they write the code, set the default values etc for nodes) and part miners & nodes who can change the values or disregard default recommendations. Same for wallets. I can disregard recommendation / default and send a free tx and hope it gets processed. Give it enough time and some times it does.