Just like credit scores. Their models aren't perfect, but the threshold for useful (for their benefit) is much lower, and profitable lower still. Since you're the product being sold and they're OK with many defects, and given that there are no financial consequences for you getting rolled up in a bad / inaccurate / predatory model, they don't care and aren't incentivized to fix it (and in fact in many cases are incentivized financially to keep it broken, since "hits" like that can be a selling point).