These were marketplaces of the polytheists, where they traded during the days of Hajj. The Companions (may Allah be pleased with them) worried that they would incur a sin if they traded in such places during the days of Hajj. So, Allah revealed this verse to show them that trading in the Hajj season does not invalidate Hajj, especially when the rites are performed as prescribed. Trading during Hajj is allowed. However, it is better to devote oneself to performing the rites of Hajj.