Why didn't the Honda dealership transfer my plates?

I'm a but perplexed as to why the Honda dealership that I purchased my 2016 Accord from didn't transfer my Mazda3 plates to the Honda; instead the business manager said that a new Maryland soundex number needs to be generated. The soundex is the number on my old Maryland License. I currently hold a DC DL. I've had a DC DL for a number of years because I live in DC and sometimes in MD. In the past I've had 4 new cars and all utilized the soundex number from my old MD license. This is very odd.

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