It seems that these 3 teams suffered defeat due to the impact of the upcoming UCL match schedule so that some players did not perform optimally. We can see from the statistics in the following picture.
Statistics Frankfurt vs Union Berlin
It is clear that Frankfurt actually has a great chance to score and even can hold the match to a draw. Unfortunately, Frankfurt players must appear to maintain their physicality so as not to force themselves to score a winning score and sacrifice their physicality. But actually this is dangerous for their current position which can provide an opportunity for Freiburg to shift Frankfurt's position.
Of course, there is an impact of the UEFA Europa League game they played in this match. The players appear so tired because there is no enough time to rest after their Europa League game against Ajax, and they need to save energy for their next Europa League game because the 2-1 win is not enough for them to make it to the quarterfinals because anything can happen. That is why some players were kept on the bench.Statistics Frankfurt vs Union Berlin
It is clear that Frankfurt actually has a great chance to score and even can hold the match to a draw. Unfortunately, Frankfurt players must appear to maintain their physicality so as not to force themselves to score a winning score and sacrifice their physicality. But actually this is dangerous for their current position which can provide an opportunity for Freiburg to shift Frankfurt's position.
This should also not be an excuse for them because they need to put more effort into maintaining their fourth position in the Bundesliga, since the teams under them are one, two, or three points behind them from the fourth position to the ninth position; any mistake of losing can drop them drastically to the mid-table.