I think everything was clear after the first game and the players of Hamburg did not believe in a positive outcome - with such a mood (objectively justified when the result of the whole season has already been lost) it is difficult to win even with a minimum score (which will not give anything anyway). Plus, by the end of the season, Stuttgart got in good shape (by the way, they took away points from Dortmund by drawing with it - as it turns out, this was way important) and therefore they easily won the second game as well.
After getting points from Dortmund and improving the quality of their games in the last few weeks, I honestly did not give Hamburg a chance in the struggle to stay in the league. It was bad for Hamburg. They will have to try their luck next year for the Bundesliga. Stuttgart once again showed how important a team they are with this win.
I did not follow this event, so I cannot say how obvious the result was before the start of the games. Maybe you remember what quotes the bookmakers had? Hamburg didn't use their chance, but they have next season and can get a direct ticket to the Bundesliga if they play well all season. It's always a safer option than trying to be successful in two separate games where you might just get unlucky.