Yes, if there was an input tag, we could tell
<Input type="submit" value= "Submit"/>
If you using button tag
Always specify the type attribute for a <button> element, to tell browsers what type of button it is.
with button tag you can provide different functionality Like submit form and reset form etc.
Don't know much about html .Maybe the reason is there are so much type of button:
<button type="submit"> submit</button>
Type attribute with value button is not needed at all for interactive UI features.
It is required only when you have a backend to listen to form submission and the button is used to submit or reset the form.