(or "The Sportsmaster? SRSLY?")
Looking at the 70s revival of 'All-Star Comics', it seems like a good idea. Much like the 80s revival of the Justice Society seemed like a good idea, or the 90s revival of the Justice Society, or the early 21st-century revival of the Justice Society, or the revival of the Justice Society that we're probably going to get in about five years when they've sorted out all the continuity fallout from 'Flashpoint' and have decided what the Justice Society is going to have been in the new DC Universe. After all, we're talking about iconic, classic heroes who've had a fan following for decades, being brought into the Modern Age with all-new adventures and all-new heroes joining them. How can you go wrong?
Actually, you can go wrong by assuming that just because a character is old, they're automatically classic and iconic. One of the big reasons that Julius Schwartz had as much freedom as he did to revamp the Silver Age versions of the JSA was because the franchises were so moribund; characters like Al Pratt and Alan Scott didn't really stir much of a memory in fans. Part of this, of course, was attributed to a general decline in interest in superheroes during the post-war era; with comics of so many other genres on the ascendancy, superheroes were considered to be kind of passe. (Looking at the newsstands of 1952 would come as an utter shock to a comics reader of today--between war comics, westerns, romances, true crime and horror comics, and sci-fi anthologies, the only heroes that could muscle their way onto the spinner racks were Batman, Superman and Wonder Woman.)
But was it really a case that superheroes were uninteresting, or was it a case of the genre not having many interesting superheroes? When you look at most of the titles that faded away, you'll notice that none of their revivals have had much success either. A Green Lantern who got their powers from a generic "magic lantern", and who owned a broadcasting company, does not have as many interesting and engaging story hooks as one who is a space cop who works for aliens and travels the universe and through time. And Alan Scott is one of the better Golden Age heroes. Al Pratt, the original Atom, is just kind of short and punches people. It's not a lot to hang your hat on.
The original Justice Society, indeed a lot of the original Golden Age characters, were the result of creators working out through trial-and-error what was interesting and what wasn't. We have been conditioned, as readers of modern comics who have seen plenty of love letters to the Golden Age, to see these as important and valuable simply because they were pioneers of the "superhero" genre, but really, a lot of them are hard to write for. It's hard to bring back villains like the Sportsmaster and make them relevant and menacing, or to make the Star-Spangled Kid seem like a sympathetic and interesting hero. The Silver Age versions of the characters can be seen as "second drafts" in that light, reworked to make it easier for writers to generate story ideas that will get the reader interested. Origins, rogues' galleries, day jobs, supporting casts...all of these need a serious rework on Golden Age characters simply to make them palatable to modern audiences.
And that's before you decide to treat their World War II adventures as canon, age them all into their fifties and sixties, and saddle them with the confusing "this all takes place in an alternate universe" scenario. Setting the whole thing in an alternate universe with a confusing backstory did more harm than most people realize; it's no coincidence that the most successful revamp of the JSA, the Geoff Johns run, took place post-Crisis. Batman will always have a more compelling origin than an adult Robin, Green Lantern will always have a more exciting reason to fight crime than his twin kids, and explaining why Superman has gray hair and can't fly is just one more thing that bogs down a story and prevents it from really getting started. The more continuity baggage your character has, the less time and energy you have to write new adventures for them.
None of which is to suggest that 'All-Star Comics' is bad. There's plenty of exciting adventures in there, and Power Girl and Huntress work effectively as a young, exciting, female version of the World's Finest in a universe that no longer has a Batman/Superman team. But the question should not be, "Why are these Justice Society relaunches so unsuccessful when they have such great characters?" It should be, "What is wrong with these characters that keeps them from working as a team and a series?" When you look at it that way, and then look at the elements of their storytelling engine, you quickly find the problems that keep the series from taking off. As long as the relaunches are determined to keep all of those elements, whether out of simple nostalgia or a belief that they're what readers are looking for, the Golden Age will forever stay a part of the past.