When you go from thousandaire to millionaire to billionare, your spending on busses or trains goes down. That's an inferior good.
Cities are not designed around the rich or the ultra-rich. Transportation systems are not designed around the rich or the ultra-rich. If all of us had infinite money we would just use private jets or something, but that doesn't mean that jets are strictly superior to cars... this is an apples to oranges comparison.
As someone who's lived in Chicago, Seoul, and South Carolina, I can say that our public transportation systems are wholly inferior to Korea and Japan's public transportation systems. It's not strictly a matter of money or not, it's a multifaceted cultural topic.
The whole idea of ranking transportation systems by what rich people do or don't do makes absolutely zero sense.
That would mean cars were an inferior good over that income range.
-> _For the ultra-rich_, trains and other public transportation are inferior options.
This is completely different from saying that public transportation is an inferior good overall. It's not that simple.
Who decides what is beneficial for me in your opinion, me, you or the government?