The two octave C major scale lesson got about 3000 compared to 48000 for Twinkle Twinkle.  This supports my personal befuddlement with why scales practice doesn't seem to work for me (or for most people which explains why Suzuki is so popular)

6 year old child:  learns scales as a series of absolute pitches that are stored in long term memory...thus develops the *unusual* ability of "absolute pitch" recognition which is only possible during early brain development.

Adult: try to learn scales like the 6 year old child but the associations of pitch and name won't stick in long term memory.   But the adult brain is good at storing and differentiating *patterns* of pitches which essentially is a strong melody like Twinkle Twinkle.

I suspect a similar phenomenon occurs with vibrato.  The adult brain is hardwired and movements tend to be symmetrical.  Move the bow faster and the speed of the vibrato wants to do the same.  Vibrato brings into the picture the issue of independent control whereas simply stopping the string with a finger is more a coordination problem with the bow and it is much easier.

Ironically, I believe learning violin as an adult should be much faster if not easier than a child if certain methods are explicitly used to overcome some not so obvious problems.