I've done some looking into this- it is accepted that potatoes are not the same quality they used to be and washed potatoes was not one of the reasons given, though I have to admit it does make a certain kind of sense. You should always wash potatoes anyway. I blame the plastic packaging as well, which has already been mentioned.
The other reasons given were:
adverse weather conditions, including both wetter weather, and drought!
The expense of using fertilisers and chemicals, making Maris Pipers especially expensive to grow.
The complex trade markets, particularly following Brexit.
The shortfall of farm workers, also following Brexit.
68% of potatoes sold are grown in the UK- the others coming from the Netherlands, Belgium and Israel. Make of that info what you will.