That can't be true, because the community is in no position to answer your question. The only people who could would be the people inside YC who actually know why they chose not to list compensation with their job ad. I don't have a clue what the answer is, and certainly nobody outside YC would.

There isn't any particular connection between how YC hires for its teams internally and what the HN community thinks or feels about such things. Both are perfectly valid questions, but they're unrelated.