laravel form bootstrap-select cant working

Question

I have a modal, with the body filled with an Ajax response.

Javascript code:

$('body').on('click','.modal-show', function(event){
event.preventDefault();

var me = $(this),
    url = me.attr('href'),
    title = me.attr('title');
$('#modal-title').text(title);
$('#modal-btn-save').text(me.hasClass('btn-edit') ? 'Update' : 'Tambah').removeClass('d-none');
$.ajax({
    url: url,
    dataType: "html",
    success: function (response) {
        $('#modal-body').html(response);
        $('.selectpicker').selectpicker();
    }
});
$('#modal-center').modal('show');
});

The url Ajax refers to this code :

<form action="{{ route('sub.store') }}" method="POST">
<div class="form-group">
    <label for="id_kategori" class="control-label">kategori</label>
    <select name="id_kategori" class="selectpicker" data-size="5" data-actions-box="true">
        <optgroup label="kategori">
        <!-- get sekolah -->
            @foreach($kategori as $kg)
                <option value="<?= $kg["id_kategori"]; ?>"><?= $kg["kategori"]; ?></option>
            @endforeach
        </optgroup>
    </select>
</div>

Why does the bootstrap-select not work? Even without the modal, the bootstrap-select works?