Eloquent Many-to-many a link not generated on create only on update

I want to set up the automatic link generation for the many-to-many relationship between Pages and Directories.

Directory.php

<?php

namespace App\Models;

// ...

class Directory extends Model
{
    use HasFactory;
    use Sluggable;
    use SoftDeletes;

    /**
     * The attributes that are mass assignable.
     *
     * @var array<int, string>
     */
    protected $fillable = [
        'user_id',
        'name',
        'slug',
    ];

    /**
     * Return the sluggable configuration array for this model.
     */
    public function sluggable(): array
    {
        return [
            'slug' => [
                'source' => 'name',
            ],
        ];
    }

    /**
     * Get the user that owns the directory.
     */
    public function user(): BelongsTo
    {
        return $this->belongsTo(User::class);
    }

    /**
     * The pages that belong to the directory.
     */
    public function pages(): BelongsToMany
    {
        return $this->belongsToMany(Page::class, 'directory_page', 'directory_id', 'page_id')->withTimestamps();
    }
}

Page.php

<?php

namespace App\Models;

// ...

#[ObservedBy([PageObserver::class])]
class Page extends Model
{
    use HasFactory;
    use Sluggable;
    use SoftDeletes;

    /**
     * The attributes that are mass assignable.
     *
     * @var array<int, string>
     */
    protected $fillable = [
        'user_id',
        'name',
        'slug',
        'links',
    ];

    /**
     * Get the attributes that should be cast.
     *
     * @return array<string, string>
     */
    protected function casts(): array
    {
        return [
            'links' => 'array',
        ];
    }

    /**
     * Return the sluggable configuration array for this model.
     */
    public function sluggable(): array
    {
        return [
            'slug' => [
                'source' => 'name',
            ],
        ];
    }

    /**
     * Get the user that owns the page.
     */
    public function user(): BelongsTo
    {
        return $this->belongsTo(User::class);
    }

    /**
     * The directories that belong to the page.
     */
    public function directories(): BelongsToMany
    {
        return $this->belongsToMany(Directory::class, 'directory_page', 'page_id', 'directory_id')->withTimestamps();
    }
}

PageObserver.php

<?php

namespace App\Observers;

use App\Models\Page;

class PageObserver
{
    /**
     * Handle the Page "saved" event.
     */
    public function saved(Page $page): void
    {
        $this->generateLinks($page);
    }

    /**
     * Generate and update links for the page.
     */
    public function generateLinks(Page $page): void
    {
        $page->load('directories');

        // Generate links based on associated directories.
        $links = $page->directories
            ->map(fn ($directory) => "https://{$directory->slug}." . config('app.short_url') . "/{$page->slug}")
            ->toArray();

        // Update the links field with the generated links.
        $page->updateQuietly(['links' => $links]);
    }
}

2024_12_20_131705_create_directories_table.php

<?php

use App\Enums\Themes;
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    /**
     * Run the migrations.
     */
    public function up(): void
    {
        Schema::create('directories', function (Blueprint $table) {
            $table->id();
            $table->foreignId('user_id')->constrained()->cascadeOnDelete();
            $table->string('name');
            $table->string('slug')->index();
            $table->timestamps();
            $table->softDeletes();

            $table->unique(['name', 'slug']);
        });
    }

    /**
     * Reverse the migrations.
     */
    public function down(): void
    {
        Schema::dropIfExists('directories');
    }
};

2024_12_20_131750_create_pages_table.php

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    /**
     * Run the migrations.
     */
    public function up(): void
    {
        Schema::create('pages', function (Blueprint $table) {
            $table->id();
            $table->foreignId('user_id')->constrained()->cascadeOnDelete();
            $table->string('name');
            $table->string('slug')->index();
            $table->json('links')->nullable();
            $table->timestamps();
            $table->softDeletes();

            $table->unique(['name', 'slug']);
        });
    }

    /**
     * Reverse the migrations.
     */
    public function down(): void
    {
        Schema::dropIfExists('pages');
    }
};

2024_12_22_140347_create_directory_page_table.php

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    /**
     * Run the migrations.
     */
    public function up(): void
    {
        Schema::create('directory_page', function (Blueprint $table) {
            $table->id();
            $table->foreignId('directory_id')->constrained()->cascadeOnDelete();
            $table->foreignId('page_id')->constrained()->cascadeOnDelete();
            $table->timestamps();

            $table->unique(['directory_id', 'page_id']);
            $table->index(['directory_id', 'page_id']);
        });
    }

    /**
     * Reverse the migrations.
     */
    public function down(): void
    {
        Schema::dropIfExists('directory_page');
    }
};