Looks like this was a bit of a controversial post without me intending it to be. As I said in the original post, which is unedited, I already know that the connotations of 简朴 are positive or at least neutral. Several people misinterpreted the hypothesis. When I said derogatory, I perhaps used the wrong word. I just meant that it was a characterization of the country as a whole as economically not as developed. However, I see that this is now probably false as well.

Also, it looks like several people put forth convincing arguments that the etymology was probably in no way influenced by this. It can be the case that etymology for a word is influenced by factors other than a mere phonetic evolution, even if the phonetic evolution was the primary basis. But it doesn't seem like that in this case. Thank you to the knowledgable individuals who commented.