Why do Turbahs have “Ya Husayn” etc on it?

This has never made sense to me. Most Turbahs I see have some form of Istigatha statement on it. "Ya Husayn", "Ya Muhammad Adrikni" (this one is from the Turbah on its Wiki article), "Ya Ali bin Musa ar-Ridha". Why is there Istigatha statements on something people use for Salaat which is only for and to Allah ﷻ , praying to and only to Allah ﷻ? We always cite the evidences that Rasulullah ﷺ prayed on Earth/soil but I feel the proof isn't sufficient if we're going to print "Ya Husayn - Turbah e Karbala'" on what we prostrate on.