That's not really an answer to my question, but I did my best to dig out the data on this.

As far as I can tell, FlixBus indirectly employs ~7,000[0] drivers, which includes train drivers. There are around 692,000[1] buses in circulation in Europe today.

So I'm struggling to see how your comment supports the idea that most buses in Europe can be monitored with GPS.

[0]: https://www.iru.org/membership/members-directory/flixbus

[1]: https://www.acea.auto/fact/fact-sheet-buses/#:~:text=692%2C2....