How is it stealing data? Most geospatial companies use OSM data, with OSM's permission, and it's a smart thing to do b/c they have a great map. Why wouldn't a mapmaker work with OSM data?
If TomTom was planning on conflating OSM data with other sources then in theory it hurts their business model because they will potentially have to make their entire map (or large parts of it) freely available in OSM.
If they can somehow set up clean room conditions and keep all their other data sources physically separated from the OSM data then it might be avoided, but then how do you do the map conflation? And that would certainly impact how quickly they can make updates.
Maybe they came up with some clever way to avoid having to contribute data back to OSM and that’s what OP means by “steal.”
They were caught red handed in 2018 i think, and blamed on some contractors. But most interesting, despite this being a widely know fact for the mapping community, i can't find any mention of it anywhere today.
There are suspicions, but no hard proof has ever been found about this.
However, there is a well-known (and non-problematic) case where OSM-data is used in GMaps. Some polish bus agency used OSM to create their GTFS-feeds, which were ingested into GMaps. Selecting the bus line will thus show an OSM-based line layer; but as that line layer is clearly attributed with OpenStreetMap, that is totally fine; both legal and ethical. See https://twitter.com/MapAmorePH/status/1453863816110952450?t=...