30-minute rule… a sign of lowering income?

Back when the ward budgets were centralized, our far-flung ward was told that when we did church-related activities, we were supposed to turn in reciepts for things like gas for our travel. People did turn in reciepts when they traveled far distances for driving youth to stake activities, etc.

I’m wondering if Church research showed that people don’t turn in reciepts for distances that were less than 30 minutes.