Because in the US, we like to feel "special" so they give us "special" names.
Acura is just Honda's "luxury" marque like Nissan/Infiniti, Toyota/Lexus, Ford/Lincoln, etc.
i.e.
Acura TL = Honda Accord with different interior/body and beefed up engine.
Acura CL = Honda Accord Coupe and same as above