why use reCAPTCHA?

i seem to have to do a reCAPTCHA test every time i do anything on the forum. which is a new feature (not been visiting for a while).
i wonder what the reason is?
i assume people know this reCAPTCHA confirmation is being sent to goolge? i had to change my browser setting to set up an account, to allow 'goolge.com' be sent information, otherwise i couldn't set up an account..

there are alternatives to this option? many open source, more privacy based options are available, which would far more aligned with what is being shared here IMO.
thanks.

I just logged in to reply and had no captcha. I'm using an android device with ALL google apps and services disabled. Using Firefox Focus as a lightweight browser.

I just logged in and had no reCAPTCHA on my desktop.

ok, yes.. i just logged in now for first time after creating new account.. and didn't have to do reCAPTCHA... maybe it's just when setting up an account. but had to do qutie a few, and because i use ublock origins, on medium mode (which is strict), i had to enable goolge.com, which i don't like doing.. but wasn't allowed to set up an account without allowing that... so this particular reCAPTCHA they're utilising is goolge connected and sending data to goolge, that's pretty clear.. just wasn't sure why they opted for that option.
but yes, seems is only for account set up.