Question

why specific heat is a different substance

Answer 1

Each  substance will have a different mass, so when the amount of  heat and the change in temperature are held constant, the only variable is the mass. Therefore, because mass is the only variable, so because  substances have different masses, they will have different specific heats.....!

Answer 2

Different substances have different mass which is variable but the heat supplied and the temperature change is always constant.
That's y different substances have different specific heat.
Hope dis helps