Properly done hammer forging arranges the crystal matrix structure of the iron and carbon in steel molecules into a very hard and durable barrel. Proper heat stress relief and cryogenic treatment further arranges austenite to martensite, hardening the steel even more and making it abrasion resistant.
Proper chrome lining (avoiding hydrogen embrittlement which can lead to peeling, flaking, and heat cracking) and you have the potential for exceptional barrels.
HK, Colt Canada, and FN make some exceptional MILSPEC hammer forged 5.56 barrels.
The Army and National Guard rifle teams often "Cherry-pick" the best out of available batches of GI-issue barrels if match rules require unmodified issue weapons (M16A2s, A4s, and M4 carbines).
Hammer-forging mass produces good quality barrels quickly.
Remember in manufacturing you can get good, cheap, and fast –– pick two.