Why are Bootstrap scripts not included?

Question

Bootstrap

Why when I specify scripts like this

<script src="{THEME}/js/popper.min.js"></script>
  <script src="{THEME}/js/bootstrap.min.js"></script>

they are not connected, but they are uploaded to the server and opened via a direct link. And when I say this:

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
  <script src="https://stackpath.bootstrapcdn.com/bootstrap/5.0.0-alpha1/js/bootstrap.min.js" integrity="sha384-oesi62hOLfzrys4LxRF63OJCXdXDipiYWBnvTl9Y9/TRlw5xlKIEHpNyvvDShgf/" crossorigin="anonymous"></script>

Everything is working. How so?