Teen Gothic

There's a gulf between Sisters of Mercy and something like Twin Tribes or Forever Grey, but we all intuit them as 'goth' and i'm just wondering how this developed, historically.

EDIT: Misspoke here, did not mean to imply that synth or darkwave is a modern thing, but more that it's far more prevalent now as a dominant goth sound and was curios as to how we still consider this music to be goth (not that i disagree with that at all).