Can't set default value for form components on RichContentCustomBlock schema (RichEditor)

<?php
/* ... */
class HeroBlock extends RichContentCustomBlock
{
    /* ... */
    public static function configureEditorAction(Action $action): Action
    {
        return $action
            ->modalDescription('Configure the hero block')
            ->schema([
                TextInput::make('heading')
                    // ->default('default value')
                    ->default(fn() => 'default value')
                    ->required(),

                TextInput::make('subheading'),
            ]);
    }
    /* ... */
}

<?php
/* ... */
class PostForm
{
    public static function configure(Schema $schema): Schema
    {
        return $schema
            ->components([
            /* ... */
            RichEditor::make('content')
                    ->customBlocks([
                        HeroBlock::class,
                    ])
                    ->columnSpanFull()
                    ->required(),
            ]);
    }
}