Is that kind of information really for sale on an individualized level, by mobile providers? Surely they have brands to protect, and don't like being sued.
The information being sold there wasn't from mobile providers, they were collected by apps. See the first paragraph of the third article: "location data quietly harvested from ordinary smartphone apps over 10,000 times". The same applies to the other two articles.
[1]: https://arstechnica.com/tech-policy/2020/08/secret-service-o...
[2]: https://www.wyden.senate.gov/news/press-releases/wyden-warre...
[3]: https://www.vice.com/en/article/m7agpa/irs-location-data-ven...