So Americans say 'herb' the french way because it's a french word', but 'taco' and every single other foreign word has to be said American style, 'tarco' as opposed to the Spanish way, which imo is closer to English tack-o.
Spanish has lots of variations, too. And the Mexican pronunciation of "taco" is closer to "tahco" than tack-o. It's a Mexican (and North American) food. So we North Americans do get a say in how to pronounce it.