I think they're gone because, within the limited time of an interview, it's hard to
prove competence with chatting, for yourself, and especially in a way that can be communicated to others in the panel. Most places I've worked, firing is a
bad bad thing. It means everyone involved with the hire failed, and morale is hurt by everyone that sees the person let go.
When I first started interviewing, this was the method I used. It turns out that most people have fanfic for resumes. "Designed a system" or "worked with a system" actually means "played an insignificant part in the design of a system" or "minimally modified some existing code". Getting to a point where this is obvious can take a significant portion of a 45 minute interview, and almost always comes from digging into the nitty gritty of the details, very close to code. Then, worried, you have them try to write some basic code as time runs out, and they completely flop, with that, and whatever small thing triggered your suspicion, being the only useful evidence you can point to for why you're saying no, even though others are saying yes.
So, I flipped it. I go for real evidence first, which gives me objective, repeatable, results, then any remaining time is left to talk and go into depth. I give them an easy work related problem, requiring realistic syntax. I've had people that were fantastic with communicating their ideas, and even pseudocode, but didn't know the syntax of a function or simple for loop, in the language of their choice. Take home code/screens can't be trusted, without basically goin through it line by line. Heck, video interviews can barely be trusted these days. I've many had people obviously, and not so obviously, copy paste the top google search result. I've even had people double team an interview, with the second person listening and typing the results on a second screen.
That said, I completely agree. My dream interview, either side, is just getting nerdy for an hour and a half with someone. But, especially for less senior roles, I can see why it's not popular, especially if you're stuck with short interviews, or are not the hiring manager, where you don't have to objectively justify things. Interviews are, unfortunately, a fairly adversarial interaction.