Hello Philander! We have another recipe on the channel which uses cloves. You can also use cloves on this recipe, reason being they smell wonderful and last several weeks.
It has to do with some sort of air flow; slowly released aroma particles. For example, an opened perfume bottle is not the same as spraying perfume on a surface (the skin). Same with just pouring fabric softer in a container, it would just not release the aroma the same way as with the salt.
You can use the homemade fabric softener we taught on the channel or use essential oils for an all natural version. You can also buy some from a health store where they sell the non-toxic ones.