all capabilities in dropdown returning boolean

I’m trying to put all capabilities in a dropdown menu. I can only get it to return boolean true (all 1s). If I do a vardump with $user->allcaps I get the actual names of the capabilities, but when I try to return them in the dropdown, it’s just boolean. Here’s my function:

add_shortcode('capsdropdown', 'sc_capsdropdown');
function sc_capsdropdown($attr) {
$user = get_user_by('id', '1');
$capslist = $user->allcaps;
$dropdown = '<select>';
foreach($capslist as $cap){
$dropdown .= '<option value="'.$cap.'">'.$cap.'</option>';
}
$dropdown .= '</select>';
return $dropdown;
}

I’ve tried using settype but to no avail.