everyone is guaranteed to buy death/funeral related stuff, not everyone wants a DNA test. Also all of that crap (headstone, funeral service, coffin etc) is bundeled together in a massive payday, not to mention funeral places tend to price gouge the bereaved. So a single death is a much bigger payday than a single DNA test.

As for the other products you mentioned, i doubt any of those companies literally only sell those individual products. They probably diversify to other products and services too.