If Casadei cannot get minutes at Leciester, maybe right now he just isn't good enough. Santos case is different as he was joining a team who are known for stockpiling players but Casadei should be able to work himself into the team if he is good enough. It shouldn't be a given that players are guaranteed starting minutes. In Santos case, he isn't getting minutes at all, while Casadei is getting minutes, just not starting because probably right now the manager does not feel he warrants starting over some of the other players who let's face it are all premier league quality.
Leicester are the best team in the Championship by far and did not lose too many key players so was always going to be a challenge to get into the team. He still can get a lot of game time. But Leicester are sitting comfortably at the top, so in this case I can't blame the manager. Casadei was also wanted by Genoa I am led to believe but no guarantee of minutes there also. He was impressive on loan at Reading who got relegated last season and did well in the U20 world cup and looked decent in pre-season, but we have not seen enough from him in a professional environment currently. This loan might show he needs a bit more time before being considered for the first team.