Google Photos was not a thing back in the days when Facebook started.
At least, even if you had it while you used Facebook, not a lot of people auto-uploaded the pictures they use on Facebook to Google Photos.
So, in that way, you must have a lot of photos that reside on Facebook. For that, Facebook has come up with a tool that will let users transfer their pictures to Google Photos.
As per the official news announcement, Steve Satterfield (Director of Privacy and Public Policy) mentioned that the tool will be initially available in Ireland.
The users in Ireland will be asked to share their feedback and depending on how the testing goes – the tool should be available worldwide in early 2020.
It is worth noting that Facebook came up with this tool being a part of an open-source Data transfer project where companies like Google, Apple, Microsoft, and Twitter have also teamed up.
Considering that, you might expect other tools from Facebook or other services to allow you to transfer your data/pictures in a way that makes sense.
For now, you just have to wait for the tool to be available for your country. You can read more details in their official blog post.