The onus should be on the hiring company to tell about themselves because they're the ones who want something. If I'm looking for a job, I can either look at the 99% of job listings (both startup and more mainstream) that will tell me exactly what I'll be working on and who I'll be working with or I can ask someone who's already been vague for clarification to decide whether I even want to apply. The incentive just isn't there for the job-seeker.

What you're suggesting is that it's perfectly reasonable for someone to post a help-wanted ad in the classifieds saying "I need help! Call me to find out what with!" and to expect people to call you instead of the ads all around yours.

Because the market for skilled software folk is very much tilted in favor of employees right now. Demand far outstrips supply. Why would a prospective (and presumably talented/in-demand) employee jump through your hoops?

When the inevitable crash comes and the supply of tech jobs tanks through the floor... then we will put up with these crappy HR shenanigans.

It's kind of like online dating. You could email a potential candidate and ask for a photo, but it's really not worth it since everyone else posts a photo. You just naturally assume that posting a generic description without a photo means they have something to hide.