Okta recently partnered with a few folks to tackle this. They published a thing [1] in April. Fraudulent registrations and bots are being screened using Shape which was acquired by F5 [2]. I'm not saying this problem has been solved, but it's an area of active concentration. For most folks, the offerings are more than adequate. For the top saas or platforms, you'll probably always have this issue as you're a lucrative target.
[1] https://sec.okta.com/shareddetections
[2] https://www.f5.com/cloud/products/bot-defense