I think a lot of the whiteboarding/leetcode stuff is just hazing, a desire for "standard" processes (every candidate has a different background, so a well-done conversational interview will differ a ton per-candidate), as a bit of a time-filler ("that's right [C-suite person who's asking questions] we have very rigorous hiring, look, it takes six hours, and see all these steps! Only getting the best of the best, I assure you."), and because if it's scripted you can have mid-level devs do it—poorly, for the most part, since conducting a good whiteboard/leetcode interview is possible, so far as that goes, but it's not easy and requires serious people skills, which is a big part of where places go wrong I think, and also tends to make it look so non-cookie-cutter that if you squint it's not really that much more "standardized" than the conversational version.
Talking about those things is a learned skill just like writing on a whitebaord. Hence why good companeis that do whiteboarding interviews also have traditional rounds. You want to give candidates multiple avenues to shine.
A casual conversation where someone is purposefully trying to put you at ease is going to be more effective at seeing someone's true skill over a whiteboard every time.
There are also a bunch of very senior people that won't play interview games at all. Especially when they're an internal referral. If I refer someone to get hired, I make absolute sure that they are not put through a technical hazing ringer. I've seen senior people who were heavily recruited walk the instant they're put into "the process" under the very sound logic of: "You wanted me to work here, so why are you making this difficult?"
When I first got into the industry, it was much more rare to have coding tests vs. just general interviews, and that meant teams often hired the best talkers or the folks who boasted the most about their accomplishments, and those two skills had very little correlation to how well someone could code.
Even worse, 'team fit' was often prioritized above others, so be it on purpose or implicitly, good candidates from diverse backgrounds were much easier to overlook. When you have the majority of engineers solely focusing on 'can this person solve a problem', it is harder to argue against strong candidates just because they look older/younger/darker/lighter/more feminine/masculine etc.
Take home tests are incredibly biased against candidates without free time, and as I've pointed out in other places, can easily be abused by spamming candidates with them which is just not possible with whiteboard coding.
Coding tests are the best way to hire, if they are done right. They aren't perfect, but so much better than take home tests and 'discussion' based interviews.