Sometimes it needs about 10 minutes to 'verify' it
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Why exactly does it take this eternity?(I got curious
) , I imagine it was clear to you after all these answers that the problem is there.
If you have to spend 10 minutes solving the captcha, I guess there is some problem at your end. It hardly takes a minute for me and I am asked about 1 out of 10 times only when I log in. We need such additional requirements so as to prevent mass registrations here. Without this image captcha, one can make 1000s of accounts here in few minutes with the use of tools of burp suite.
The captcha comes from Google, and it gets more complicate and slower to solve if your connection is less trusted. I assume OP uses Tor, and indeed, it can take very long to solve. Even worse, it can end in a timeout too.
As LoyceV already stated, it takes longer when you are using "abusive" IPs. (Tor, Free/common VPN ips.)
As to why, probably because google doesn't want to have bots registering hundreds of gmail accounts/spamming their search engine ( although the latter seems a bit far-fetched, but is something that you'll endure aswell, it will think you're sending "automated queries", ( probably because there are so many people using that one IP at the same time.))