Because within the past five years, Sega only releases crap.
That makes...absolutely no sense. If everything SEGA released was considered by 100% of the world's population to be crap, then you might have a point. But guess what? It isn't.
I assume you are trying to make the argument that Shenmue III would see a drop in quality since you believe everything else SEGA has done has experienced the same drop. But again, that is a blind guess, and Yu Suzuki has a near perfect track record when it comes to video games.
I'm not saying I lost hope in Sega. I'm sure they could release great games in the future. Most of the games (not all) that have been released in the past five years have been remakes of other games or games that are generally based towards children. Making an hd release for Shenmue II has already been done. Making one for the original would be odd because Sega should have done that before making the second game, if that is their plan. As far as making a third game, it would require a lot of money, a very large team, and Yu Suzuki would also need the "ok" from Sega. Does anyone else not think this is a bad idea? Why would Sega want a game series that they created specifically for their own consoles to be released on another companies console? It just wouldn't make sense. Especially after 15 years.
No, most of the games are not rereleases or kids' games. If I wanted to, I could easily prove you wrong with the FACTUAL release list, but I'll leave it to you to do your own homework and see how horrendously off you are on this one.
An HD Shenmue II? You mean the North American version that was basically ported? They worked on that for less than a year. It's hardly an HD remake.
Your last three sentences finally are starting to make a little bit of sense. You see, SEGA, like all corporations, want to make money more than anything. If Shenmue sold like Sonic, you'd best believe that there'd be a yearly game, along with Shenmue Tennis, Shenmue Racing, Shenmue Rhythm Game, etc. It doesn't matter what console it was released on, they already broke that rule with Shenmue II on Xbox. They couldn't care less about the Dreamcast anymore when it comes to exclusivity. That thing is a decade and a half old.
Also, Suzuki has already said that SEGA is not the problem, it is the money. And he may not need the 300 member team that he used before, since a lot of the concepts Shenmue pioneered have been explored in other games.