Moderators frequently remove questions from the HNQ. Our site is large and provides many interesting questions. The number of questions per site is limited. Removals increase the turnover of math-questions in the HNQ and thus allow more math-questions to get known network-wide.
Put differently it seems better to have eight questions there for three hours each, rather than one for a full day. Except maybe if that one question is stellar, and thus likely to be much better than those that will replace it; with all due respect that does not apply to yourthe question you mention.