The biggest reason should be that they're just bad. They gather sus data from their undersized sensors, then derive tons of sus insights to overwhelm you. None of it is accurate enough to base major life decisions on, which is also laughable because even if it were accurate, there are effectively no major life decisions to make based on the data! Here I can save you $500: Go to bed before midnight. Set your alarm at least +8 hours from when you lay down. Sleep in a cool, dark room. Eat nothing 4 hours before bed. Don't exercise 4 hours before bed. Limit alcohol. Engage in at least 30 minutes of strenuous physical activity each day. Done.