Honestly it's mostly about looks at this point. Modern glue is strong enough that the headband is just a nice finish. It's a detail, not a dealbreaker.
Seriously, does it actually matter that much? I've got notebooks from craft stores without them and they're fine. Even some of my old books have falling apart headbands but the spines are still solid. People get so hung up on traditional methods when the basic glue and stitching does the job. It feels like making a problem where there isn't one.