The effort put in is negligable. The spammer is often something called a 'bot'. A bot is a bit of malicious programming that, once released, has a life of its own on the internet. So beyond the initial work coding, there is no effort.
As for the gibberish, I can only guess at corrupted files, or a file that has been put into a computer, got itself encrypted and then pushed onwards.
With aritificial intelligence (AI) these things can recognise it is being asked a question, and attempt to answer it; often succesfully.