Just sitting here laughing at the mere suggestion of forgings....lol
Costs aside: you realise there is no benefit to forged receivers other than weight.....right? Even weight-wise you're looking at only 1-2 ounces max per set. Theoretically they might be slightly stronger, but they wont wear any better. And if you have a catastrophic failure, it's still going to kaboom.
The only reason that companies forge ARs is due to quantity. There are untold millions made and sold. Small runs? They would never have made dies in the first place.
Also let's not forget that the only reason the modern sporter exists is because the AR15 is restricted. They would not sell worth a damn in the U.S
**EDIT** Not because they are inferior but because they cost more and do the same thing.
You do realize they are stronger, lighter and cost less?
So how many more reasons do you require that some want forgings?