Because Reply tool inserts its buttons as <a class="dt-init-replylink-reply">Reply</a>, they are not focusable from the keyboard and therefore can’t be used by those navigating from keyboard (including, but not restricted to, some screen reader users). The easiest fix to it is to add href attribute, which won’t be entirely accessible (since this is not really a link, but a button), but will be an improvement nonetheless. To make it more accessible, the link should be replaced with a <button>, since it triggers an action and doesn’t navigate anywhere (it can look like a link if you want).