There are practical reasons to designate the difference between hard and soft maple when it comes to kitchen utensils, but that is the only place one usually sees specification in marketing materials. While Hard Maple is considerably harder than Soft Maple, the latter is still a hardwood and more dense than Poplar.
For the purpose of this cremation urn, there is no practical reason to specify and it would be easier and less expensive to simply say "Maple" and use and deliver the least expensive material - Soft, in this case.
Aesthetically, they are different enough that we don't feel comfortable not offering the add-on of choosing "Hard Maple". The association with "cutting board" and "bowling alley" might not sit right with some patrons but others will desire that almost pink/peach light cream/white that Hard Maple exhibits. Soft Maple is a more yellow cream to white and has a propensity for mineral streaks and interesting pinhole character.
Because Hard Maple only comes from one species of Maple tree, it has a price premium. Soft comes from a variety of Maples and is more abundant as a result.