why due to lones pair resonance basicity decreases

Basicity of a compound is a measure of compound’s ability to accept the proton(H⁺).For ex- amines behave as bases because the lone pair on N has the capacity to form co-ordinate bond between the nitogen atom and the proton.Similarly in aromatic amines,the basicity depends on e- density on nitrogen.Higher the e- density on N more will be the basicity.In aromatic amines,the lone pair of electrons present on N is delocalized,hence e- density decreases due to resonance so basicity decreases with the resonance.In general---
Basicity is inversely proportional to the number of resonating structures.For ex-basicity decreases in the following order--
C6H5NH2 > (C6H5)2NH > (C6H5)3N because the no. of resonating structures of three are 4,7,10 respectively.