Dumpster rental is a price-and-availability decision
Someone renting a dumpster is usually mid-project and mildly stressed. They want to know three things fast: what sizes you have, what it costs, and whether you can drop it when they need it. Sites that hide all three behind "contact us for a quote" lose to the competitor who published a size chart.
This is one of the few trades where publishing pricing genuinely wins work rather than inviting haggling, because the product is standardized and the buyer is comparing.