Tafseer Ibn Kathir of AT TAUBAH [87]

رَضُواْ بِأَن يَكُونُواْ مَعَ الْخَوَالِفِ وَطُبِعَ عَلَى قُلُوبِهِمْ فَهُمْ لاَ يَفْقَهُونَ

They were satisfied to be with those who stay behind, and their hearts were sealed over, so they do not understand.