I've worked as a programmer mainly at companies in Silicon Valley. I've taken and given plenty of whiteboard coding interviews, including for Google.
The problem is that they were designed originally to find recent college graduates who have topics like red-black trees or counting sort at top-of-mind. This process weeds out older folks who might have a lot more practical knowledge but aren't as well versed with more academic topics that aren't encountered much in the real world. Instead, people are given an expectation that they need to brush up on their academic skills for a non-academic job interview, which is an indicator of a broken process.
Besides, even Google has publicly admitted that there is almost zero correlation between interview scores and the resulting job performance score. It's disheartening to see that they really haven't revisited this process then, despite their claims of data-driven decision making.