European countries have made diesel cars part of their strategy for meeting their engagement under the Tokyo accord. As such, diesel fuel is less heavily taxed then gasoline (except in the UK) as an incentive for consumers to use diesel and emissions standards are set with an eye to promoting the use of diesel. Additionally, almost all the diesel fuel in Europe is in fact B5, meaning in contains at least 5% biofuel.
By contrast, no such advantages exist in North America where diesel often costs more than gasoline. Our emissions standards seem to have been designed specifically to keep diesels out or to make them so expensive that consumers are not interested. One exception is Québec where almost half of all VW's sold are TDI's and it would probably be even more if dealers could stock more of them.
As for the Fiesta, it will be returning to these shores later this year after a two-decade absence, but only in gasoline form. None of its diesel engines meet US emissions standards and the demand for diesels does not justify the expense of certifying them.