If you're in your 50's, do you remember when Sony had three stereo product lines in the early 1970's: Marantz, Sony and Superscope?
Why do they do it? Ask 'Lincoln, Mercury, Ford', 'Acura, Honda', 'Lexus, Toyota', etc. Gibson guitars has a cheaper line, Epiphone.
What do they say? They try to make your cost no object equipment to see what they can really do. Then they try to develop reduced models so that they can compete in different target markets.
Sometimes they don't want to have their name, like Levinson, associated with lesser than reference quality. They'll create another company, like Proceed, that's not associated with reference quality, just very good quality.