I would think they are guessing most people's passwords are weak or something. Like a screen pattern is weak, can be broken in just 300k attempts or maybe less because people use the same patterns and people can't be bothered to use passphrases.
With a 6 digit code cracking it will take close to a year on average. With your screen pattern example it's around 100 days. That's more than enough time for the owner to notice and turn on anti theft features. Maybe even for the police to find and return the phone.
I would say pins are even less secure because people usually set it up as something like their birthday and thieves also often simultaneously steal some id card in a wallet which has exactly that.