I'm not sure about Shiozaki, but Morishima got buried by Michael Hayes because of all the Terry Gordy comparisions people like to make, and Vince didn't think he was marketable.
Well that's a shame about Morishima cause I think the WWE could use a big guy like him as a heel. Ryback looks like it he's not working out along with Mark Henry and Big Show being faces now.
As for KENTA, I would've been extremely surprised if they offered him a contract. Like it said before in the thread, it seems to me that they are putting a cap limit on the smaller guys in the company.