Quite right! One of the major style guides in the Humanities recently updated theirs to 4th edition (MHRA) and now mandates DOIs with every citation to a journal article, claiming that most if not all publications have one. Some sample checking of a major purveyor of online material in my field (JSTOR) suggested that this really isn’t true, though they offer ‘stable URLs’.
This is still a very unstable field with at least three classes of links: regular URLs, DOIs, ‘stable URLs’, and OP suggests none can quite be trusted.