Actually, playing in bot lobbies is just like playing in a training mode. To begin a controlled Battle Royale round, click on the "Battle Royal Practice" button. Here, you'll play a Battle Royale simulation against AI opponents who are all at each other's throats. The Bot AI is a little easier than usual.
Online gamers usually log off at ungodly hours, such as early or late evening. If you play Warzone at these hours, chances you will get bot lobbies or be matched with low-level players.