What is particular about this area that draws these thugs here as opposed to the Forest Hill end?

The Honor Oak end is closer to Peckham.

Eh? So the "thugs" are coming from Peckh'm, then jumping right over the leafy streets of Peckham Rye and parts of East Dulwich, only to descend on HOP. I think not.

More likely scenario - Honor Oak Park (the B238), as it slopes down from Francesca Cabrini towards HOP station (as I understand, most of the mobile-muggings have happened on this stretch?) is bordered on one side by the cemetery, and One Tree Hill, both of which have some dense bushes and trees, and a few dark corners where it is quite easy to hide and wait for people to walk up or down the hill.

A few years ago had long walk in One Tree Hill and noticed undesirable elements entering from the other side.