Just picking up on this one point, though not wanting to go off-topic - TfL's travel research shows there are certain demographics (lower income backgrounds and black passengers) who disproportionately use the bus even when it's not the best value or most convenient way to make their journey.
They struggled to get to the bottom of the reason for this, particularly on the cost front, but did note the following, which is going to affect migrants more (who are in turn more likely to be on lower incomes):
That quote was from research in 2012 mind, so may be less relevant in the world of Google/Apple Maps/Citymapper/etc.
Agree with your post though. And I've travelled enough on long distance trains and Megabus/Flixbus/NX long distance coaches to know that there are plenty of people who would take the train for long distance journeys should it be more affordable (and publicly recognised as such).
Not to mention that it would help our environmental impact, given long-distance electrified rail trumps coaches for emissions. They fall behind for shorter journeys running DMUs. So if anything, the long distance journeys would help us more with our environmental targets, as well as making comfortable travel more affordable for passengers, regardless of level of income.
I think the research may well be relevant.
A lot of usage is probably down to perception, so if some sections of society perceive the railway as being expensive or for rich people, they may well choose the bus even if it's poorer value.