These corporations can pay people to develop Free Software. They do in many cases. And when you are paying someone to do the work, you can dictate the conditions and practices of that work (e.g. If you're not using Copilot, you will be replaced by someone who will gladly shit out 100x as much code as you).
But an innumerable amount of responsibilities in the Free Software world are not paid. And you can't force a volunteer to use LLMs if they are convinced it is a socially and ecologically poisonous technology.