[eropple]

You're replying to someone who explained to you that that question is, in many quarters, a question about socioeconomic status, and your reply is "I don't understand why it's rude, it's not a question about socioeconomic status." Yes, it is about socioeconomic status. You may not think it should be, you may not like that it is, but it is, otherwise people would not take it as such. The reasons are historical and cultural, and if you study the (American, though not exclusively) relationship between work and sociological sense of self of the 20th century you are surely more than capable of divining the details, but it exists, and your further confusion about rudeness will probably continue until you accept that the measuring tools of rudeness are not yours to calibrate.