So, why did the T2CAS not alert the Test Pilots to the impending ridge?
Probably because the ridge didn't have a transponder! Having seen this level of muppetry on the first page I've looked at, I think I'll leave again
Maybe you should look up the acronym.
TēCAS is an integrated TCAS plus TAWS system by Thales. So it should have warned of impending terrain collision, if (a) it was not disabled, (b) it was loaded with maps of the region, (c) the maps of the region were accurate and (d) it was receiving accurate GPS coordinates.
Neither of which we know for certain just now.