As for someone who did followed Mangagamer blog or tweets(and the forums before it got bombed and still haven't recovered T_T), Da Capo III is a huge game. The prologue itself is big, The common route is also big. Overall DC3 is pretty much comparable to more or less Koihime Musou length which was the longest VN MG had worked on at the time. IIRC, perhaps Koryuu has compared words length of DC3 to LOTR novel length.
As for 3 years, Koryuu is the only assigned translator on it and it's mainly because for keeping the translation quality consistent as opposed to 2-3 translators on the project.
The point is: DC3 was never expected to be released within small timeframe after its announcement. And people who may want something similar to Da Capo has Princess Evangile for their fix. But most important of all, MG Project Status is steadily updated so people knew of its progress.
Well, aside from cons, SP did announce titles outside of them after all, and people may be including what accumulating to "announcing too much" backlog.