The small renters aren't the problem here. It's accounts like this using Splex (or something similar) with almost 15k cards that are listing hundreds, if not thousands, of 1 bcx cards. The 1 DEC fee per card listing/transaction on an account this size is negligible when you're raking in 115k DEC/day.

Check the collection and sort by level to see for yourself: https://peakmonsters.com/@smalp/cards

The number of transactions this account makes for price updates and cancellations is astronomical.

Scroll through a page or two and see for yourself: https://hiveblocks.com/@smalp