Lapua doesn’t make Dasher brass. They make 6BR brass that we all blow out to Dasher. As to why they don’t make it? Eh, no idea, but I expect they have ran the market research to know what brass they can sell at their target margin, and the cost it takes to produce said, and decided it doesn’t pencil out in their favor.
Norma does make Dasher brass, but of a different dimensional spec than what most of us use for Dasher reamers.
A few outlets do hydroform brass for the Dasher, Hunt’s being a very popular one. The downside, they cost the same $1/each plus 55¢/each for the hydroforming service, so most of us don’t end up using them.