It's estimated that there's at least 13.7 million illegals in the USA and American Immigration Council estimates that it will cost $315 billion to detain & deport all them from the USA which is just too expensive, but according Grok it will cost only $81 billion to detain & kill them in gas chambers which is clearly much cheaper solution. The USA also doesn't have to negotiate with the other countries to let them accept their illegals back.