Why does bromine add faster to a trisubstituted double bond than a monosubstituted double bond to produce dibromides?

Bromine is identical to an alkyl group, thus, on the basis of Markovnikov's rule, the ions of bromide are more probably to combine to the carbocation, which exhibits the majority of the alkyl groups.  

The disubstituted alkenes exhibit two alkyl groups in contrast to hydrogen bonded to the alkene. The monosubstituted alkenes only exhibit one alkyl group and the rest of the bonds are for hydrogen.