mass update only saving one record laravel

i have method to mass update the studentSection table. This method works. But if i mass update multiple records only one record gets save.

Update (latest)

public function setStudentsSection(Request $request)
    {
        $enrollments = Enrollment::whereIn('student_id', $request->students)->where('session_id', $request->session_id)->get();
        $program_section = ProgramSection::withCount('students')->find($request->program_section_id);
        if(($program_section->students_count + count($enrollments)) <= $program_section->max_students) {
            $data = [];
            foreach($enrollments as $enrollment) {
                $data[] = [
                    'student_id'    => $enrollment->student_id,
                    'enrollment_id' => $enrollment->id,
                    'section_id'    => $request->program_section_id,
                    'created_at'    => Carbon::now()
                ];
            }
            StudentSection::createMany($data);
        }
        return response()->json(['errors' => ['message' => 'Selected Section is full.']], 405);
    }

Second approach: This works but it does not trigger my observer that outputs message. Assigned student to section

public function setStudentsSection(Request $request)
    {
        $enrollments = Enrollment::whereIn('student_id', $request->students)->where('session_id', $request->session_id)->get();
        $program_section = ProgramSection::withCount('students')->find($request->program_section_id);
        if(($program_section->students_count + count($enrollments)) <= $program_section->max_students) {
            $new_student_sections = array();
            foreach($enrollments as $enrollment) {
                $data = [
                    'student_id'    => $enrollment->student_id,
                    'enrollment_id' => $enrollment->id,
                    'section_id'    => $request->program_section_id,
                    'created_at'    => Carbon::now()
                ];
                array_push($new_student_sections, $data);
            }
            return StudentSection::insert($new_student_sections);
        }
        return response()->json(['errors' => ['message' => 'Selected Section is full.']], 405);
    }

Here's my relationship

Enrollment Model

public function studentSection()
    {
        return $this->hasOne('App\Models\Student\Section');
    }

StudentSection model

public function enrollment()
    {
        return $this->belongsTo('App\Models\Enrollment', 'enrollment_id');
    }

Third approach

if(($program_section->students_count + count($enrollments)) <= $program_section->max_students) {

    foreach($enrollments as $enrollment) {

        $enrollment->studentSection()->create([
            'student_id'    => $enrollment->student_id,
            'section_id'    => $request->program_section_id,
            'created_at'    => Carbon::now() //optional
        ]);

    }

    return response('success');

}
return response()->json(['errors' => ['message' => 'Selected Section is full.']], 405);