Core developers can not just change the nodes because they want, don't you see it takes years to implement segwit? which seems useless due to most platforms are not using it. You should know better why we have to pay fee, because bitcoin require miners to solve the blocks and it's not easy as you need ASICs which takes lots of money. No one want to mine bitcoin if they are not paid, Satoshi Nakamoto has made the nodes works this way to ensure bitcoin's environment could run and last as long as possible.