Maybe you haven't heard old Tristania? There is nothing pop-metal about them. Nothing that would lump them in with bands that I would put in that pop-metal category like Lacuna Coil, Within Temptation etc. And I find it hard to say how they are gothic when everything about them is gothic - the atmosphere, the keyboards, the violins, the vocals, the lyrical and musical themes (ie Poe), the appearance (though obviously that counts for little). Certainly more so than bands like the Cure, who are basically a gloomy pop band who wear makeup.
Ok, maybe Tristania wasn't the right comparison then, the other bands you mentioned are probably better examples of what I was getting at. But generally, it seems like whenever there's a band that has a female singer with operatic vocals and plays more or less symphonic pop-metal they are known as gothic metal, and I've just never understood that.