There is a chance of that yes.
The insurer discussed earlier itself says on their website the following
"arson is often as a result of the actions of an individual and with no clear trends. This makes proactive action to protect church buildings even more important"
Furthermore they specifically give tips on how to protect churches from arson, including "to make the church look as busy as possible, use the building as much as possible for church and community activities".
This alludes that this is down to boredom/pyromaniacs who wouldn't attempt it if there were people regularly using the church.