Currently worker ants of most species share only three quarters of their genetic code. It seems like worker ant clones would be better, as it would remove all genetic conflict of interest between them. Then they would be like our body cells. Only queens (and possibly males) would be produced sexually.
why has evolution not produced perfect X can usually be answered by the correct mutations have not occured. evolution is about jury rigging good enough not perfection.
you are assuming ant are free to change how related they are, they aren't, they cannot rebuild their reproductive system from scratch they can only modify what they have.