The current specifications in terms of efficiency classes are internationally standardized. As far as their implementation is concerned, it is up to each individual country to decide when which legal measures have to be enacted and strictly complied with.
The successive increase in energy efficiency classes involves a great deal of effort for suppliers, but also for customers.
Manufacturing and certifying the engines requires a lot of resources and drives up costs. Customers also have a great deal to do when integrating new products into their existing applications, often in modified dimensions, and when ensuring that “old” engines can be replaced by new ones if something breaks down.