why carnt i put the seed straight into the rockwool?

There is another good reason to not start seeds in rockwool - breach birth. Sometimes the cotyledon, or "head" gets stuck in the rockwool & just a bent over stem will emerge. Then, you will have to perform surgery to get it out & that doesn't always go well.

I prefer to start in rockwool...no issues and simple, water it just once, place seed in, put in dark until it pops up, then move to light