We like software engineers because they can synthesize complex software architectures, whereas someone with only networking knowledge will be at a much larger knowledge deficit on most software focused assessments.
Infosec has trended toward application focused security for many years now.
In an hour you can go over only a finite amount of knowledge, I was asked about aspects of technology I knew very little about because I hadn't tried anything in that space (FWIW it was a segment of networking). To pass over candidates based on a minuet lack of detailed knowledge - to me is crazy.
It's like interviewing a builder and asking them if they know where the majority of local maple wood comes from. Who cares, and if you need to know - Google it! Great, now you know more than you ever needed about the local maple industry!
YMMV, sample size 1, etc
Conferences are great for networking and entertaining. They're not great for learning new stuff, there's much better media out there. I'm not sure what your gripes are with it.
For infosec, the hiring bar is entirely random. Know your algorithms as those questions are all still fair game, know an enormous and entirely random amount of security trivia as infosec has interviewers with incredible ego, be able to solve CTF challenge problems under extreme pressure in 30 minutes, be able to review code in all programming languages for security defects, etc. I recently had an interview for a IoT penetration testing role (requiring C and Python) at a large tech company. The first phone screen was an engineer on an unrelated team asking me Java OWASP Top 10 style questions. What on earth???
Apparently CTFs (which do nothing except teach you how to get better at CTFs) are the new hiring bar. God only knows what's next.
So don't feel bad. Keep interviewing and you'll get lucky. Luck has far more to do with it than anything else at the moment.
Most organizations are not equipped to hire for one-of roles on dev teams involving information security.