"And yet, coding agents are nowhere near capable of replacing software developers. Why is that?"
Because you will always need a specialist to drive these tools. You need someone who understands the landscape of software - what's possible, what's not possible, how to select and evaluate the right approach to solve a problem, how to turn messy human needs into unambiguous requirements, how to verify that the produced software actually works.
Provided software developers can grow their field of experience to cover QA and aspects of product management - and learn to effectively use this new breed of coding agents - they'll be just fine.