It's my impression that people tend to underestimate "junior engineers" in the C++ world. I'm always impressed at conferences that there are so many young people holding presentations about really advanced topics.
IMHO this "no junior will ever understand that" attitude comes mostly from older folks who learned C++ as C with classes and to whom even the STL is a work of the devil.
Those people giving talks at conferences are the best of the best. 99.99% of people who write C++ have no interest in the arcane depths of the language, and would rather things "just work" over having a library that does something cool, but hard to debug when things go pear shaped.
Not all, the people giving talks are just people who happen to be interested and curious.
This idea that only the best of the best are able to be curious and learn the nature of the tools they use at a very deep level is misguided and furthermore promotes a kind of anti-intellectualism.
It's also a large part of why I think many developers get burned out, imagine working in a culture with other engineers where people are kind of pressured to only do boring work, stick to boring features, only write code in a very narrow manner that satisfies the lowest common denominator using the same old boilerplate over and over again and keep doing that for a decade or longer versus an engineering culture that values people being inquisitive, breaking out of their comfort zone, writing interesting libraries that abstract out common patterns and eliminates painful repetition, and who appreciate the inherent complexity of challenging problems instead of treating it like some arcane voodoo that only the select few can understand.
IMHO this "no junior will ever understand that" attitude comes mostly from older folks who learned C++ as C with classes and to whom even the STL is a work of the devil.