IGMP snooping prevents report suppression
Multicast hosts won't reply to a membership query message when they see a membership report from another host:
However, switches with IGMP snooping enabled intercept membership reports from hosts. This means that hosts never see each other's membership reports, and all of them will send a membership report (instead of one per group).
The switch ensures that only a single membership report is forwarded to the multicast router.
Links: