"LEADER!"
"Get over here! We need to defend this as much as we could!"
"No! We can't fit that many adventurers in here! Just get out of here!"
"We can't! We can't fail now!"
It was the twentieth wave, and at this point, there were only two posts left. These posts belonged to Albrecht's group and Isaias Asclepius who single-handedly defended his post. Then again, it was thanks to Albrecht's contributions that he managed to defend his post until the twentieth wave.
In short, the other heroes failed to defend their posts, and it was a great blow to their pride. As such, they retreated towards Albrecht's post and invaded Isaias's post as well. Instead of taking a strategic retreat, they decided to defend the two remaining posts even though they'd already failed to defend theirs.