When websites get a ton of traffic the concern is that the algorithm that find fake data will not be accurate and start blocking paying customers. So it's a fine line between blocking paying customers and fake data. What these algorithms do instead of blocking is to throw captcha's so if the traffic is really human, the captcha can be solved. The bigger problem is that there's a good chance that humans who are thrown a captcha will leave to go buy somewhere else (either because they are lazy, the captcha is hard, etc...).

Solutions like CloudFare and Distill have sophisticated algorithm to balance out fake and real data but even they are not close to being perfect.