One of the reasons espers are so important is that they're the only ones left who can craft sophisticated machines and technology. There are no fossil fuels in Heyoke's world. If you want a plastic-like material you need a trained esper who can transmute it for you. That's why any existing espers are automatically made citizens of the republic and forcibly trained. We see from Majorodomo's perspective that the entire country really only had a handful of highly trained espers left, and they can't maintain the economy on their own.