Unfortunately, the interesting guys to fill such a forum do not hang out on social platforms and bikeshed a lot. They are busy. Usually you can find a few on project specific forums/mailinglists.
I've seen all of those topics you mention gain traction, probably with the exception of "climbing the career ladder at big corp", but that's the broader Zeitgeist not just HN.
The way to get more C++/Fortran/Java discussion on HN is to submit good relevant content. If you post something really really good, sometimes the James Gosling of X shows up to comment because HN's diversity keeps them around. But any really good topic is likely to draw comments from people who worked with the James Gosling of X because HN has a lot of those people.
HN has grown large enough that there is an audience for just about any tech topic so long as the resource is reasonably good...in fact, that's been the case for a long time, and this from someone who was posting articles about Windows and Microsoft in the days where every time the Macbook got a new 8% faster Core 2, the front page of HN was dominated by the press release and Ask HN was full of "are you upgrading?" treads.
In the end, finding or creating good content is the way to increase discussion of the topics one finds interesting and to influence the direction of the community.
If you are more prone to be personally expossed trends start to matter more and influence which stacks you'll get involved into.
Sadly that has a self-serving foundation but, what can you do about it? In the other hand, happily, disruption is healthy.
I'm genuinely interested about topics you would like to read about/discuss in these areas.
BigCorp other than Google and Apple is underrepresented. Where are the guys who produce 5 billion lines of COBOL each year hanging out? Where are the SAP and IBM programmers?
Many of us also highly value work-life balance. As another commenter suggested, after 5pm I'm probably not on HN and am instead traveling, out to dinner with friends, playing sports, reading some good fiction, or whatever else is interesting this week (and before 5pm, I'm working...) Personal projects take up only some of my time. After a little while, much of the conversation here has become annoyingly tepid and it's only the rare tech-related post that I give more than a quick skim.
Edit: I will take issue with the sibling comment that for us, it's just a job that pays the bills. At least in the office I work, there is a very high professional level; we take pride in doing good work and maintaining that level, in keeping up with the state of the art, and implementing best practices. Myself and all my colleagues are all passionate about our work and it is definitely not "just a job". In my personal case, I'm fulfilled enough with my day to day work and develop as a programmer enough to take pleasure in having a varied and full personal life.
Not talking about programming outside of their workplace, in my limited experience. At least for the ones I know, programming is not a lifestyle, it's just a job that pays the bills - they care about doing it well, then leave to meet their (non-programmer) friends and talk about anything else (sports, politics, etc). As far as I know, none of them frequent community sites.
Probably running the big-ass ERP systems [0] on big-ass IBM mainframe iron on behalf of Apple and Google....their dirty little secret no-one is allowed to talk about.
:)
[0]: https://en.wikipedia.org/wiki/Enterprise_resource_planning