I would just have assumed that the cost of a dvd edition is literally peanuts now, so even selling cheaply and in low numbers is just profit.
After all, the encoding is to a legacy and mature format, and is already digitised for the (U)HD versions, the programming (menu and structure) is far simpler, the licence and fees are already paid, and the disc manufactories are already there to get a bit more out of their existing equipment.
My version of the question would more be “how are there still DVD manufacturers when there’s so little profit / value in the product?”. But I guess that question is answered by the existing machinery and the alluded continuing volume / demand.