There are lots of Software and Bots which are made to create account and do a lots of automation process. They are not the humans so that's why website owners put captchas in their website to prevent these bots from doing their job. That's why these captcha entry work companies invented. They hires people who wants to do simple work so they created API by which that automation software can submit captcha to you and you can solve that captcha and submit back to that software of bots.