Historically, captcha was crowd sourced training for OCR that happened to present to the trainer as an test that they were not a bot. That became training for A

Historically, captcha was crowd sourced training for OCR that happened to present to the trainer as an test that they were not a bot. That became training for AI image classification and collecting this data was way more important, valuable, and under the users radar than to present them with ads. I can't say for V3, but I'm guessing that collecting data for prediction is still more valuable than presenting the user with V2 images with ads.