Legally how?

OSM has a two-way data sharing agreements directly with (among others) Apple and Bing/Microsoft. Additionally, the "Overture Foundation" with members including AWS/Amazon, Microsoft, Meta, and TomTom have a complicated indirect two-way data sharing agreement with OSM. (Overture Maps are a "curated" subset of OSM data and members are encouraged but not required to make contributions and updates to the maps directly upstream to OSM.)

Google probably sees their data as a moat and likely aren't interested in two-way data sharing. (Given how many of their competitors are now involved directly or indirectly with OSM or Overture, they may be correct.) OSM probably can't legally scrape it without an agreement in place.