Actually it does. You are being naive if you think it does not.
Sunnis destroy the graves of personalities that Shias adhere to. Hence, the issue.
Maybe because certain muslims start to cross the thin line between respect and somewhat shirk, when they start chanting certain stuff while visiting the shrines, or asking of the dead, what even alive cannot do.
As i see it, there is a very fine line between respecting and worshipping. In ignorance and lack of religious literacy, folks will start to kiss the stones or collect the dirt, or bow. Trust me, it happens. Maybe that's the reason for it.
Or it's just simply to accomodate pilgrims. Allah knows best.