I don't know the reasons why it's been removed, but to use it again, you need to include
"illuminate/html": "@dev"
within your composer.json require section, then in config/app.php update the providers array to include 'Illuminate\Html\HtmlServiceProvider' and the aliases array to include
'HTML' => 'Illuminate\Html\HtmlFacade',
'Form' => 'Illuminate\Html\FormFacade',