This was the second such move to change diesel fuel, after the initial push back in the early 90s that removed about 90% of the sulfur from diesel - requiring that refineries cut sulfur from 5000 ppm to only 500 ppm. Now the EPA wanted to do it again, but this time even further, to go from 500 ppm to just 15 ppm.
To be fair, nobody's complained since about the environmental effects that the sulfur cut had. Millions of tons of sulfur have been prevented from entering the atmosphere in that time. But the users of diesel fuel recognize the potential problems that taking the sulfur out would have on the diesel engines specifically. Looking past the fact that "ultra low sulfur diesel" was more expensive to product (adding 5 to 25 cents per gallon to the fuel cost), the bigger concern was the new fuel's effects on engine parts like injectors and fuel pumps - parts that relied on the fuel's natural components to help lubricate them. They were concerned about ultra low sulfur diesel lubricity. The industry held its breath as they envisioning blown injectors and broken down engines in critical situations.
The fuel refiners had to scramble to provide solutions for consumers (diesel fuel users are the consumers in this case). This is where diesel lubricity additives come in. The newly created need in the marketplace forced refineries and fuel suppliers to use more lubricity additives to ensure these ultra low sulfur diesel fuels didn't destroy engines. Refiners typically choose from either synthetic or mono-acid technologies to treat the fuel. Mono-acid treatments (the name refers to the type of molecule it is) were introduced in the early 90s specifically to combat the effects of the first 90% drop in sulfur. Because they are more the industry standard, mono-acid diesel lubricity additives are the least expensive. This contrasts with synthetic lubricity additives which came along somewhat later. Proponents of synthetic lubricity treatments pay a little bit more but may prefer to do so because of the reputation that mono-acid lubricity treatments have for causing a handful of undesirable interactions "downstream" from themselves. In other words, synthetic lubricity additives have fewer problems (they also require less treatment to get the same effect) but you pay a little more for that benefit.
Other posts you may be interested in: