Could you explain why it is?

Sure. If you don’t add a comma, Python would not recognize it as a tuple. See the following code:
Python 3.8.2 (default, Mar 26 2020, 15:53:00)
[GCC 7.3.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> (5) == 5
True
>>> (5, ) == 5
False
>>> print( (5) )
5
>>> print( (5,) )
(5,)
>>> type((5))
<class 'int'>
>>> type((5,))
<class 'tuple'>