It's a good idea for the people with GPU miners to share or leak them. Block rewards are small, and the FUD is hurting the price and any profits you make with a GPU miner.
We are talking about humans here. Humans are by nature greedy, selfish and only interested in advancing their own interest at the expense of others. Most people do not care about anyone else but themselves and will do anything and everything to keep their advantage at all cost. Here and there there is someone that is actually willing to give, share or help others, but they are very very rare. This selfish attribute of humans is what is making crypto a dark and ugly place as they don't mind killing a coin as long as they can make a few buck before they move on. It is what is driving the behavior in crypto 99%.
So you are basically saying a dev should just put up their miner that they took the time to develop that could have been hours, days or weeks for free. Would you work for free?
Ask a dev how much donations they get from miners that use the ones they openly update. As far as I know there 2 or 3 that do. So the same can be said about miners. They use a dev's miner without contributing anything back.
If I remember correctly sp_ has increased his x11 miner over a year now and said he has less than 2 or 3 BTC in donations. Think about that for a minute.
It's not a perfect world but there are two sides to every coin.
People should be rewarded for their skillz and it is so that those with skillz will prosper over the rest. Sometimes though whats the point if those skillz give you an advantage that becomes no advantage at all. Lets use an analogy - one sports team buys all the best players and keep winning game after game, year after year. Soon there will be no more spectators and no more tickets sold because the people lost interest causing the good sports team to have to let the players go because they don't have enough money to pay them anymore. Let GPU miners get their advantage early on for their skillz but at some point open it up, otherwise what is the point if people leave and those 3 will be the only ones mining with no-one to buy from them.