I cannot imagine the value to the company from whatever usage data they get from their toothbrushing app is anything close to the value they get from selling brush heads. So it would be immensely foolish to lock down the toothbrush.

The app is a selling point, and they do it because others do. Without it, they’d lose the portion of the market that wants to track which parts of their mouth they’ve brushed properly to their competitors. But that isn’t their main market, and they’d be idiots to kill their product chasing that niche.