Is this because there are not even ten Jewish males in the city, the number required to form a synagogue?
لِذَا ٱعْتَادَ سُكَّانُهَا ٱلْيَهُودُ أَنْ يَجْتَمِعُوا عِنْدَ نَهْرٍ خَارِجَ بَابِ ٱلْمَدِينَةِ .‏