@praxeology There once was a legitimate reason, for phishing prevention - showing you some information specific to you entering your username, so that a phishing page would need to actually talk to the origin server and couldn't just be a static page or simple script, making it harder to build one.
But now with ready-made phishing toolkits being widely available, and most split-form sites not actually doing the 'showing information about you' bit, I don't think that's the reason anymore; my suspicion is that the newer cases are the outcome of "UX" folks who entirely rely on A/B tests... which often results in weird and frustrating outcomes like this.
@Rairii @praxeology That seems like it could be done much better by dynamically replacing the password field upon detecting an affected username