The first spill containment products for drums were very tall in order to meet the required gallon capacity specified by the EPA regulations. Many pallets today are still relatively tall (approx. 12-14" for 4-drum models and approx. 16-17" for 2-drum models). In many situations and applications, this height is not an issue. If drums are loaded and rarely used or simply stored on these spill pallets until they are needed, it's really not a big deal.
But for those applications where drums are being moved on and off the pallets with any kind of frequency, that height can become very significant, very quickly. The other potential issue is the height at which a taller spill pallet can put the top of a drum. If hazmat is being poured into the drum, or dispensed out of it, that height can put splashed or spilled liquid right at eye level.
The Ultra-Spill Decks offer a very low profile (5 3/4") to make handling much easier. It also lowers drum tops so that they are not dangerously close to eye level.