"If neon is so abundant, where did it all go?"

I'm guessing more or less where are the helium went. Off into space, because He's molecular weight of 4 is insufficient for terrestrial gravity to hold it in the atmosphere.

Neon's weight of 20 doesn't seem to be quite sufficient to keep it floating around earth, either. Molecular nitrogen (N2) is 28 on the scale, and that gas is more than plentiful, so the cutoff must be between the two.

Because both He and Ne are noble gases, they can't generally react with other chemicals that might weigh them down sufficiently.

Argon is the next noble gas in the series--it's sufficiently heavy (40 daltons) that it isn't going anywhere, and in fact composes 1% of the atmosphere.

Most of the H2O, O2, N2, and CO2 in our atmosphere was produced by outgassing from volcanoes. (A popular model also says much of our water came from comets.)

But Neon does not form chemical compounds, so it is not bound to comets or associated with rocks from which to outgas.

Neither is it produced by radioactive decay, as is Argon.

So the earth started with very little neon to begin with, and hasn't captured or produced more over time.

See http://www.vanderbilt.edu/AnS/... and http://www.scientificpsychic.c... for example.