Humans are lazy. The average person who steals a bike is not going to pull out a Bluetooth sniffer. And if they did, they would probably find dozens of nearby devices (try it yourself - I just did and have 53 Bluetooth devices near me).

Thieves will, however, reply to an alert that says there is a tracker following you and hit the "disable" button. Friction is key. Google and Apple are making it extremely easy for thieves. We are pushing back on this.