Alcohol is an organic, non-polar compound. The components present in herbs are also non polar. And like dissolves like...
As to why this happens, is because of polarity. The forces due to dipole-dipole attraction make the molecules that are polar to dissolve in polar solvents. This means these compounds interact with water, easily forming bonds to dissolve.
Non polar compounds, having no partial charges cannot interact with polar solvents and hence prefer non polar solvents.
There are some exceptions to this rule, though.
http://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text11/Tx112/tx112.html