To summarize your point (and correct me if I'm mistaken), Apache httpd is legacy that people don't seem to want to make the effort to move off of, but still want the benefits of nginx, so they'll stand up nginx in front of httpd, rather than migrate off of Apache (and update their platforms to support that).
I feel the "marketing" concept is less actual marketing and more feature appeal, but I guess that's similar? Maybe not, though. Features provide actual value, whereas marketing is ... tricksy.
Apache httpd "legacy"? Seems a bit exaggerated. As far as I can tell it works just fine, have plenty of very good tutorials(like those from digital ocean), performance wise no problems(at least for our usage). And seems simpler to setup.
At my work we use IIS for our main website, but I've been asked to setup and configure a few wordpress installations. I've played around with both nginx and apache, but it was much easier to find clear instructions to setup wordpress on apache, so thats what I went with. I also really like apaches .htaccess support. Easy to lock down access to wp-admin by just dropping a .htaccess file in there restricting access to local ip range, instead of having to pollute the nginx config file with that sort of thing.
"works just fine" is completely orthogonal to "legacy", same as "well documented", etc.
The way you're writing, you sound like you've tried one (Apache), and not really the other (nginx) and are basing your opinion on that, not on any merit-based evaluation...
I feel the "marketing" concept is less actual marketing and more feature appeal, but I guess that's similar? Maybe not, though. Features provide actual value, whereas marketing is ... tricksy.