“Others in the Twitter discussion noted that WCEU has been moving more towards non-tech topics over the past few years and other major WordCamps like WCUS have also been part of this trend.”

It’s not just WordCamps, but in general, WordPress has become unwelcoming (if not hostile) to PHP/backend devs within the last few years. All WP blogs out there are mostly covering Gutenberg stuff right now. If I need to get info about more advanced topics I have to resort to StackOverflow.