phpseclib 2.0 can not use Composer to create autoload

PHP Snippet 1:

composer require phpseclib/phpseclib:~2.0

PHP Snippet 2:

/var/www/html/vendor-downloads/
- composer.json
- composer.lock
- vendor/
  -- autoload.php
  -- composer
  -- paragonie
  -- phpseclib

PHP Snippet 3:

- phpseclib/
  -- autoload.php
  -- composer
  -- paragonie
  -- phpseclib