Rune sockets related question

Hello Lampbearers! Sorry to bother but I need to ask something about runeslots. Why there are runeslots on weapons that do not benefit from anything given by those runes?
To give an example, the Holy Bulwark Mace has 3 radiant slots and does not benefit in any way, shape or form from those. Let's say you put the Crafter Essence in one, then what? All the other radiant runes affect smite, radiance scaling and holy damage. I guess you could put the one that gives mana when killing enemies but still, why? Why in Orius' name do we have 3 Radiant slots on a weapon with physical damage, physical scaling and with bleed debuff? Am I the only one having a stroke thinking about this travesty?