I think you're overestimating the content of the initial message from the recruiter to the potential candidate.
If someone gets three messages a day, five days a week, and 80% of those messages say "there is a job somewhere, I won't say which country, or what kind of job, but it's a leading-edge company that won awards for excellence in 2015, would you like to jump on a call?", that's not enough information to decide whether to jump on a call.
Let's focus on just that 80%, because that's what's being complained about.
The potential candidate has no idea if the call is worthwhile yet.
But from experience, the potential candidate should estimate: It's probably in a city, state or sometimes even a country, that they aren't going to relocate to. It's probably offering less than half their current salary, or if they are not currently working, it's probably offering at the low end for what they could get. It's probably in an area of technology that has almost no overlap with what they have done before. It's probably not an interesting job even if everything else were great. The recruiter has probably not read your profile at all. Their message is probably somewhat automated, and you might not even get a reply if you say yes to a call.
Given that it's a recruiter who has already shown how little they value your time (by sending a message devoid of useful information, when they could easily say useful things up front), and in some cases they have lied ("I'm a headhunter and my client specifically asked me to write to you" in their mailmerge template...), but they have whetted your appetite enough to reply - it seems only fair to reply with a few easy questions first before a call:
- Which country? Would I have to relocate? Is the salary less than half my current salary? Is it a tech job? Is it a management job? Is it a retail job? Have you looked at my CV/profile at all? Am I writing to a human being?
You're right that a quick call is an efficient way of imparting information. But who's going to agree to a quick call about something extremely vague when the other party has shown so little consideration towards the potential candidate so far, and there's almost certainly nothing in it for the candidate?
It's analogous to agreeing to a sales call which was proposed by an opening message like "I have a household product you will definitely want to buy - tell me your number so I can call you!!" with no clue about what the product is. Of course you're going to be curious enough sometimes ("whetted") to reply with "tell me something useful about the product before I agree to a call?" It's amazing how many of these get a second message that's just as vague as the first one.
Perhaps this strategy works out for those recruiters, as it will filter out candidates who feel comfortable declining low quality approaches, and appeal to the more desparate candidates who will take anything. Recruiters are often looking for candidates that would accept below-average salaries to work for less attractive jobs, after all.
It's still reasonable for a potential candidate to get answers to a few basic questions before proceeding with a call.