They were satisfied to be with those who stay behind, and their hearts were sealed over, so they do not understand.
The Saheeh International Quran Translation
رَضُوا۟ بِأَن يَكُونُوا۟ مَعَ ٱلْخَوَالِفِ وَطُبِعَ عَلَىٰ قُلُوبِهِمْ فَهُمْ لَا يَفْقَهُونَThey were satisfied to be with those who stay behind, and their hearts were sealed over, so they do not understand.