That and the fact to not release a game within a week's time of a heavily anticipated title such as Kingdom Hearts II, only to repeat the feat with Dissidia: Final Fantasy. As you mentioned, imagine how many people could have played the demo had it been included with MGS. Plenty of gaming mags also hand out demo discs, I don't recall any of them being on there either. What about E3? Game Expo?
With V though, I think the bad sales was caused by a variety of issues. First of all, the poor reviews on Suikoden IV which a lot of people bought after the success of the first three games and also the lack of any media exposure and the fact that it was overshadowed by Kingdom Hearts II. Heck, a mate of mine didn't realise Suikoden V was released until two months later. Sure, it could be his lack of looking up, but if you frequent games websites and none of them mention it, because they're all about Kingdom Hearts II, it is easy to see why.
Either way, Konami had no real reason to doubt Suikoden. The first three titles were met with good reviews and the only thing hampering the sales were Konami's lack of promotion and the fact that the games were released in limited quantities to begin with. Maybe they just doubt themselves, resulting in some poor decisions. I mean, they don't have to go all out on the E3 saying: "HERE IS SUIKODEN VI, ENJOY!!!!!!!!!!!" But if we saw last year's (or the year before, whichever) press conference... /facepalm. "Here is N3 2! Yay! Applaude, please" *clap* *clap* *clap*
Bandai Namco spends more time promoting Ridge Racer, a launch title for new platforms. Gee, Konami. Step it up.