Have they told you that they feel insecure dating a man with a lower income or are you projecting that?
She has told me about how her coworkers make fun of men behind their back when their wives are promoted to higher positions than them (e.g., things like "we know who's in charge of that relationship"); asks me questions like how would I afford to pay for my parent's cancer treatment if they were to get cancer; reminds me I will not be able to afford a house while her friends are buying houses; has expressed dissatisfaction for me preferring designer Uniqlo collections rather than actual designer clothing; and has given me a hard time about being in a low income field (not studying CS or engineering).
edited: I thought of more points to add.
Meanwhile, my gut feelings about this say that I wouldn't want my partner to feel this way about my income status.
To bring things back to the original question, I think this whole experience has made me skeptical of people who optimize their life around income (past a certain point). At the same time I think chasing a higher income is probably an addictive to some degree, so I understand how people can fall into that and I think it might change people (my girlfriend obviously was not like this when we met).
My takeaway as a low-income person, is that I think high-income people will always dismiss me if I make these types of statements. "Of course he thinks this way, he's just a poor a student!". It's this kind of tautology that makes it impossible to deny being an alcoholic, etc. As far as I'm concerned, from my current position, it is impossible to persuade anyone that is dismissive about low-income people to think otherwise.
On the other hand, I might be giving young me too much credit. I was stubborn as hell and had a lot of other shit to get rid of too! Aging is a hell of a process and I highly recommend it!! :)