reCAPTCHA used to be integrated, but it had several problems. For some users there were timeout issues with no way to do proper debugging. Posting an issue on github got no reply, so support is poor.
It also uses a third party service from Google, and I see no reason to have 30.000 websites use a third party service, when it can be done locally.
Please be aware that any CAPTCHA is to be used as a last resort. It will give a bad user experience for many users. You really don’t want to use it unless spam really gets out of hand with no other solution working good enough.
There are many anti-spam features available, you should use them, and see what works best for you. The order in which they are listed in the documentation is from “very much advised” (Nonce, Honeypot) to “ill advised” (CAPTCHA).
If it were up to me the CAPTCHA would have been gone already, but apparently some people want their visitors to have a bad experience, so it is still in.
