I think the reason for no large scale installation of Microwaves is weight. Also, the existing system of cokk/chill/reheat has been around for a long time and is used around the globe. For a carrier to introduce a new way of doing meals? Problems and cost from the ordering of the machine, till selling it on.
It will be much cheaper to stay with the status quo and fiddle at the edges for Y. Simpler to alter for C + F. Which is why we've seen the lounge menu leap forward to solve the problem.