She does not allow you to wear the ashes for the same reason she does not allow you to cut off grandma’s finger and wear it as a necklace - to do show would show disrespect for the body. It is why She requires cremains to be buried or interred in consecrated ground, the same as a body would be.
Relics of Saints are placed in altars (
ewtn.com/library/liturgy/zlitur80.htmt) and venerated for the benefit of the faithful. They are treated with the utmost care and respect and are not worn as jewelery.
In short, cremains and relics are apples and oranges with different rules governing each.
What is
really bothering you?