That's not always what is going on. In some cases unscrupulous operators will run through large numbers of $1 transactions in order to lower their chargeback rate.
Chargebacks have a cap, if you go over that cap you get fined or lose your merchant account. So in order to dilute the pool they'll make a lot of low $ amount charges usually masquerading as some charity, those will have very low charge back rates so the average charge back %age will drop.