While one could go into great detail, the quickest reasons would be the following:
1) "psych" illness is much more common than "neuro" illness
2) Disability/mordibity is greater from psych illness than neuro illness
3) The number of psychiatrist in the country is about 10-fold greater.
Someone else chime in, but would it be wrong to speculate that there are still more biological unknowns in psychiatry than neurology? I'm under the impression that neurology is a somewhat more static field in comparison.
Because the NIMH, NIDA and NIAAA have more money than little old NINDS. This relates to the fact that psychiatric illnesses, especially if you include substance use disorders, cost society a good deal more than neurological illnesses.