If you are running mysql or postgres on a public ip address it would be equally stupid and irresponsible regardless of the useless default password that many people never change unless you also set up TLS properly (which would require knowing what you are doing with e.g. certificates). The security in those products is simply not designed for being exposed on a public ip address over a non TLS connection. Pretending otherwise would be a mistake. Having basic authentication in Elasticsearch would be the pointless equivalent. Base64 (i.e. basic authentication over http) encoded plaintext passwords is not a form of security worth bothering with. Which is why they never did this. It would be a false sense of security.
At some point you just have to call out people for being utter morons. The blame is on them, 100%. The only deficiency here is with their poor decision making. Going "meh http, public IP, no password, what could possibly go wrong?! lets just upload the entirety of linkedin to that." That level of incompetence, negligence, and indifference is inexcusable. I bet, MS/Linkedin is considering legal action against individuals and companies involved. IMHO they'd be well within their rights to sue these people into bankruptcy.