I think conclusions that 2e was not a success are flawed. TSR didn't suffer because of 2e. TSR suffered because of really bad business decisions (like flooding the market with unsold novels that murdered the profit line of the company). I think people look the company struggling and assume the edition struggled as well. I think for the first time, D&D had real competition in the 90s, with the rise of goth and emo culture driving Vampire and Werewolf to strong popularity. And Magic took off, taking a lot of casual D&D players with it. But I don't know how 2e could have captured that market without doing a completely different ruleset.
So I think 2e did about as well as you could expect, considering the environment of the time, and any struggles of the company are related to other poor decisions from TSR outside of 2e.
I think there are a lot of misconceptions about the rise and fall of particular editions. The very original rules had done well enough that Gygax could do advanced, hard cover books. He also wanted a definitive edition since groups were all playing with their own house rules. Gygax considered Advanced to be especially important for tournament play. Basic was for more casual players, but the term basic turned some people off.
2e came out because TSR had booted Gygax out of the company. 2e did well, especially with supplemental material, but was up against stiffer competition, and criticism that it had not modernised enough. It's main problem, however, was the extreme mismanagement of TSR.
TSR dies. WOTC buys DnD, and creates 3e. The rule set is brought up more to date, and the OGL goes gangbusters. The OGL bursts. 3.5 is still doing well, but sales have slipped, which is inevitable. Fans seem open to idea of new edition, and WOTC is hoping for another spike in sales that a new edition brings. 4e is born, but it feels very different from traditional DnD, and players leave the game in waves. Still has its' fans, however, but not enough to make WOTC happy. Their old system is being adopted by Paizo, and eventually PF becomes number one.
WOTC drops 4e suddenly, and 5e is announced. By this time, the WOTC staff is very small, and they ha e to proceed cautiously, not sure if they can recapture the market. This is the reason for the slow release schedule, and comments about getting game right before adding more options.
None of the above has anything to do with dying from an overabundance of material. Sure, companies run into trouble from over extending themselves, but that has never been the case with DnD. TSR overextended with novels, Hollywood trips, pulling up sunken ships, and other crazy ideas, not the game itself. Paizo has been bringing out a steady stream of products, after all, without killing themselves.
5e is doing well, because it feels like DnD again. It is simpler and more streamlined, which is what players want these days. Geek is hot, which is serving the game well. I assume that sales will slip eventually, and we'll have 6e. New editions are good, however, or we'd all be still scrambling to get a hold of those original little booklets, and playing fighting men all wielding d6 weapons.