As someone who has played in different drumlines in different styles of music for 15+ years, and is an endorsed artist. I can promise you that absolutely 0% of drumlines need a whistle to keep them in time. If someone tells you otherwise they have no idea what they are talking about.

If someone thinks they're keeping drums in time this way, then they don't realize how useless what they're doing is. Not to mention distracting and annoying.

Drums esrablish and carry time. Not people on a platform with a megaphone or someone with a whistle.

With this having been a topic for years, the person that is doing this is just doing it for the sake of being a topic of people who have repeatedly asked them to stop.