They just don't have access to giant pools of residential IPs, so too many sites end up blocking all the cloud providers by IP range/ASN anyway, even if they could get through a captcha.
google has a large amount of "caching servers (GGC)" located in data centers for residential providers all over the world.. They use these servers for a variety of services.. Most of the traffic I have seen from them have been for their "URL preview" service ..
They just don't have access to giant pools of residential IPs, so too many sites end up blocking all the cloud providers by IP range/ASN anyway, even if they could get through a captcha.