ReCAPTCHA decided to start charging for their service (which they have every right to do, but it was a surprise). Just to use ReCAPTCHA on our Free customers would have cost us $10M+/year, which was untenable. We’d been concerned about the privacy issues around using a Google service for some time, and this was the kick in the butt we needed to move off of them.
hCAPTCHA has been incredibly responsive so far to improving their service, something even at our scale we had a tough time getting from the ReCAPTCHA team.
Ultimately, we’re working toward entirely eliminating visual/audio CAPTCHAs. But, until then, we are enjoying working with the hCAPTCHA team.