The big issue with seed starting mix is ensuring it is weed free, if you make your own compost it's never clean , unless you do it on a industrial scale, and if you heat treat it, the microorganisms are destroyed. When you buy it the origin is unsure and it could have been shipped a fair distance, like coconut compost.
Mushroom and worm compost, which are almost double worked compost are excellent, but there's not a unlimited supply and again availablity depends on your location.
What is your solution?