Their first stop is probably a Google search: "example job description software engineering"
Then, they replace the buzzwords with their own buzzwords, which they probably already know, and they're done. This takes much less time than scheduling time with the engineering team, and since they'll be doing the interviews anyway, what's the harm? Their part of the job is already done.
The second part is that companies are doing the same thing that applicants are doing with their resumes; they don't want to put any red flags out there, in order to keep their possible pool of matches as large as possible. There's a chance they can persuade you to ignore a red flag if they talk to you; if they list it in the job description, there's a 0% chance.
Examples of information that might be excluded:
> where is this?
- It's in the suburbs outside Reno, NV.
> exactly what is the work I’m supposed to be doing here?
- You'll be maintaining our undocumented, 12-year old legacy backend.
> What’s the team? 4 beginners? 4000 experienced devs?
- I literally have no idea, I was just given a budget and a number of slots to fill.
> What tech is used
- Something you've never heard of, running on top of PHP 4.
> what is it about my skill set that makes me a good fit?
- We will literally take anyone who can FizzBuzz.
Finally, there are some dog-whistle/shibboleth phrasing that seems perfectly clear to the person who wrote the description, but might not be clear to you. Examples:
> “You’ll work with the core of our digital strategy”
- You'll be working on our product that is the closest to making money (or actually makes some! who knows).
> “You’ll work close to the systems”
- You'll be doing some DevOps as well.
> “You’ll have a central role”
- We have a small team.
And so on.