Whiteboard or not, in any interview, you are judged relative to performance of other candidates. At very coveted places like FB, they don't have a dearth of candidates. i.e. Even if you did "good enough", very likely they'll find someone who "aced" the same question on the whiteboard. (We're not debating whether that's right judgment or not, but from their perspective, it's justifiable).

Having said that, I believe that your hunch is also correct viz. tech interviews for core roles at good companies these days, are more competitive than ever. Compared to say 10-15 years ago, the variety of interview problems is higher, complexity of software has increased, and the value of an engineer is understood to be higher ($Millions in equity). All that is contributing to moving of the goal post.

(Source: several years of doing this, now running an interview training course for a living http://InterviewKickstart.com).