That would be okay but that would just kill cryptos ....99% of the population of the world could not code to save face. All your doing is encouraging more of "people with get more and people with not get nothing"....not the way you want to start going.
On the other hand, I do think people need to be more open and donating to devs for the work. I just started to do that myself because I understand many things come with a cost, and the devs take time to make such a good item for all of us.
If you don't already think there are probably more with their own code improvements and tweaks who are not releasing or even saying anything publicly you are crazy.
Now you may be right at this level of the average 100 sat low end coin, they aren't investing the time or effort on a wide basis, but I guarantee you that anyone running a million dollar bitcoin server farm isn't releasing their code if they find something that makes theirs faster.
The info slowly gets out and becomes common knowledge for the most part, and then to support the masses they would release their code to move the 90% up to all the same level, but there is no way this isn't already the 'norm'.
They will release it and make sure the public at large has the tools to keep enough support for the market to keep it profitable for them, because you are right that a broader market is healthier overall, but it is in their best interests to do so only once they have accumulated enough coins and are going to profit from it.