You have indeed helpfully given one factor in the under-representation of minority ethnicities in cycling, essentially about the cultural attitudes to wealth, status, and the behaviours that indicate wealth.
Having identified that one, valid, factor, you seem resistant to exploring other factors. One can't help noticing that the factor you are comfortable in identifying and discussing is to do with "them" and if it is to change, it is "them" that must change. Your resistance seems to be to identifying factors that are to do with "us", where, if change is to happen, it would be "us" who changed. That could just be laziness and complacency - self examination and change are always hard work, and it's so much easier if we can put the onus on someone else. In this specific case, however, it is unavoidable that there is an association with race: the people with whom you identify the problem as resting with are BAME, the people you are resistant to recognising any problem with are white.
The use of "ethnic" to mean non-white, which has cropped up in this thread, is pretty incontrovertible evidence that the factors are not just to do with "them": there are indeed factors to do with "us" that, whether deliberately or unwittingly, display racist attitudes. We can debate how significant those factors are in comparison to the other, perfectly valid, factors that you have identified, but we can't exactly deny that they are there when they've been posted on CycleChat and defended when challenged