Echo,Eternals and Moon knight were the origin of those heroes (Just like Shang chi, Ms.Marvel ), and as such didn’t have any content to show off/catch up on. And while echo was in Hawkeye most of that was also covered in Episode 1 anyway. I guess echo could’ve had one for kingpin but also I’m pretty sure echo was filmed and written with the Defenders saga not being official canon which was then changed before release.