The decision comes at the right time. It is right before halftime of the season and Union Berlin was 4th in the table I think after 8 games. Now they dropped to 12th and didn't win a game in a very long time as Soonandwaite mentioned. If they decided to find the right moment to act, then it was now. They gave him two months or a bit more than that to fix the problems, but if he can't do it and the management knows that Union Berlin can do better than that, then sack him.
In the 2022-23 season, Union Berlin was in fourth place in the table. And this season, Union Berlin competed for the title. However, in the last season, we saw a bad decline in Union Berlin's performance. In the last season, Union Berlin was in 15th place in the table. This season too, Union Berlin is not able to do well. And now the Union Berlin management has decided to fire coach Bo Sevennson. I don't know if this is the right decision. I don't think that changing the coach will improve Union Berlin's performance. Along with changing the coach, the Berlin management should take the necessary steps to strengthen their squad. If the squad is not strong, I don't expect good performance from Union Berlin.

haha oh my gosh this is hilarious, please be honest how well do you know the Bundesliga? You said that Union Berlin was competing for the title and I can tell you this is the funniest post I have read in a while. I follow the Bundesliga for many years now and this is why I post in this thread because I know a couple of things about it. If you have no idea what this league is about and which team is competing for the title or not, why bother posting here at all... Union never competed for the title and they won't be competing for the title.
You are now repeating what everyone else has already said, but the reasons are manifold. Though the coach is the first one who is going to get sacked, but behind the scenes arguments have been going on for a while whether the transfer decisions were bad and they were. Union Berlin has no striker anymore that scores consistently and since they let Sheraldo Becker go to Real Sociedad in 22/23 without making sure there is a good replacement for him, Union Berlin's offense was garbage.
Last season they scored 33 goals in 34 games and now they are on the way to be even worse. This begs the question whether sacking Bo Svensson was enough or whether other people in charge should have been fired, too.