I suppose they feel that people don't care that much about butter so the cheapest (but quality) option is best - President is part of the largest dairy firm in the world after all.
There isn't much in the way of a large brand that's truly British that could compete - it'd probably have to be Dairy Crest with their Countrylife product.
Any smaller brands (like they've done with the Roddas clotted cream or FeverTree tonic) are probably seen as not worth the extra expense.