The ISI website provides some indication of the factors involved with
a relatively young journal (such as SJ) being indexed in their system:
" For brand new journals, the editors examine the publishing record
of the journal's authors and editorial board members, noting where
their articles have been published and if their work has been cited."
No doubt the professional reputation of the many fine scholars and
researchers on SJ's editorial board, across a wide range of applied
disciplines, had an important role to play in this decision.