The babies are tender. Fertilizer can burn.
Further, seeds don't take in fertilizer - grass does. If you throw down fertilizer with seeds, it may be more than a week until seeds germinate and two weeks until you see the tiniest blades of grass. During this time, you are watering once or twice a day. What happens to all of that fertilizer? Does it just get washed into the subsoil - on its way to our drinking
water? When the grass is ready to take it in, will there be any left?
The truth is so freakishly complicated, it could fill volumes of
books. It depends on the kind of seed, the kind of fertilizer, the amount of water, rain, what all is in the soil, the temperature, etc. etc. etc.
So, it is true that some folks make recommendations that are different from mine. My general rule of thumb recommendation without knowing lots more: hold off on fertilizing until the grass is ready for the first mow. By then, it won't be so burned by it, and it will be able to take it in. Usually, there is lots and lots of other stuff that used to be growing in that spot that has recently died somehow and the baby grasses can
feed off of that.
Naturally, given a freakishly huge gob of details on a situation, I might change my recommendation. But if we're gonna go into that much detail, I wanna get paid. Lots!