Parmandur
Book-Friend, he/him
We don't know the number, but irnia entirely conceivable thar TPP margins on a D&D Beyond sale may be larger, due to logistics and distribution.You pay a cut to sell your product at someone else's store, whether that store is a FLGS, Amazon, Roll20, or DnDBeyond. I don't see how WotC expecting a cut is problematic, and clearly the folks entering into these deals have concluded that it makes sense for them, as well. To a person, they seem delighted at the opportunity.
Buying, operating, and expanding DDB is not free, anymore than running a FLGS is free.