>Doesn't Flixbus cap their fleet to 100 km/h?

And the train is even slower than that. Let that sink in.

>Graz–Vienna is admittedly a bit of a special case

Special case at being ripped off when flights from London, Paris or Berlin across the continent are cheaper than trains from Graz to Vienna.

>The train makes up for that in views, though ;)

It really doesn't when you factor in the ticket prices. Some people who are not tourists use transportation out of necessity to get from A to B as quickly and cheaply as possible, not to do sightseeing and die of old age, so speed and value for money is more critical than what you see out the window. And a significant part of the trip is through tunnels anyway.

And there's only so many times you can see the same hills and houses before it gets repetitive and you go back to your phone. Not to mention if you travel second class, trains on that route are typically full of loud obnoxious people talking on their phone on speaker mode, who don't have courtesy for others so it ruins any enjoyment of sightseeing unless you have good noise cancelling headphones.