Why isn't random.randbytes() not secure if the seed can be both time or entropy from /dev/urandom?

/dev/urandom is used in the much more recommended secrets.py library. It is also said that random module makes use of either current time or the system entropy from /dev/urandom. Then:

• What seed does it use by default? Is it time or entropy from /dev/urandom when I do not myself define a seed?

• If it uses /dev/urandom by default then it should be as safe as secrets module.

Ps I have looked at a similar question that was asked. My curiosity still wasn't full-filled as the former question remains unanswered.

This question only came up after I looked at https://github.com/tna0y/Python-random-module-cracker