It’s a subjective listing, started early on, that’s more based on popularity (at the time) than anything else. Forums for Emory, for example, are much more active than the one for Tufts. It really doesn’t mean anything.
If the start adding colleges to these list, they would be swamped with “Why not my college!” request, so it’s best to leave it be…just think of it as a “sampling” of colleges…