Most of them do. Which the article fails to mention unfortunately. You not only need the tools, you also need to be in a network that allows you to forge sender

Most of them do. Which the article fails to mention unfortunately. You not only need the tools, you also need to be in a network that allows you to forge sender IPs. Filtering those has been advocated for a long time (BCP38), but unfortunately there are still networks that don't do it.