When I see full stack in job descriptions, it implies that management doesn't really know how to invest in order to develop the product that they're trying to develop. Looking for a full stack engineer, really means that the management is looking for a superhero who can magically solve all their problems.
A full stack developer makes sense for a very small web application that doesn't really do much, or as an overall architect when the plans include scaling a team to meet the diverse roles needed any more complicated application.
The thing is that, any application of sufficient complexity to solve a tangible need, has problems and details that are beyond the scope of what one engineer can do. Ultimately, modern economics comes from specialization, and that means that successful development requires team members to specialize in the various components of a complicated web application.
If an application can really be built by a full stack engineer, at this point is it truly unique enough compared to what's already on the market? Perhaps? If the founders are able to determine that such a market exists for such a simple application, then they are probably smart enough to write the application themselves!
Back then, websites scaled more slowly, there were no mobile clients, and simple UI was fine. We could cut corners by mixing php, html, and SQL into a single file; but if you do that today you won't go much further than a hackathon.
Now you need a web site, API, mobile apps on both Android and iPhone, and maybe a desktop app. Tolerance of bugs is lower, so developers need to spend more time writing automated tests. The "web site" might be a mix of an in-house app, crm, blog, Facebook page, ect. No "full stack" developer can do all that in any reasonable time.
