Because blaming Brexit is a convenient excuse to grab more money. They were not the only company to do so. Considering the use of off-shore accounts and shell companies, tax breaks, investigations in tax avoidance, and then hiking the price on very old hardware - Apple has zero excuses. I don't really blame them for not wanting to pay taxes to a war monger government, but the consumer shouldn't be punished.
Convenient excuse? Or convenient reason? Apple is a company to make money. As long as currency is a reason to raise to price in UK, why not? Anyway, it still means that the price change is due to currency.