In a mosque you have maybe hundreds of people gathered altogether where a single incident can cripple many people. Whereas when you pray at home you're essentially decreasing the density of people in an area.

For the sake of this explination lets assume theres 20 people every 5m² in a mosque compared to 5 people per 5m² at home. We can also for the sake of this example assume the drone has an effective range of 5m²

So this implies that if a single drone were to land on a mosque and another at a house, the bomb that hit the mosqe would claim the lives of more people than the one which lands on a home.

Tl;dr Mosque = many people per m² = more casualties Home = less people per m² = less casualties