Germany still does this, to a good fraction of incoming long distance busses (but not trains IIUC)
Last year my bus took nearly an hour to get across the Serbia-Croatia border, which is technically a Schengen border, but Serbia is surrounded by Europe so security is usually lax. We all had to get off and go through passport control while the police combed the bus. Meanwhile, car traffic was being waved through without the slightest formality. Infuriating.
At the supposed non-borders within the Schengen zone, police are increasingly present. Often they get on buses (and trains) just to check out the passengers, obviously looking for passengers with migrant profiles.
Two or three years ago I crossed the ultra-low-security Germany-Denmark border on a local bus. There was no border security but I overheard the driver making an intentional phone call to someone to say that he had a foreign tourist aboard. Schengen has not completely abolished borders, alas.
And yes, border controls are almost everywhere again.
The literal Nazis made a law that virtually banned long distance busses inside of Germany, and the market was only liberalised in 2013. Deregulation and liberalisation often get a bad rep, but they have done a lot for us.
(To be more precise, the Nazis didn't outright ban long distance busses directly, what they did was give the government railway monopoly a veto over most bus routes and lots of extra restrictions. Which amounted to the same result as a ban. Just like the US doesn't directly ban buying from the world's most popular electric car brand or importing photovoltaic cells: they just slap outrageous 100%+ tariffs on them.)