German here: There are two kinds of ID, our normal ID card, which everyone has and the passport, which is rarer. We can travel to the whole Eurozone + Turkey + most of the Balkans + Switzerland + Norway with the ID card, so basically to most of Europe which is currently not at war. Many people don't own a passport, because they can travel as much as they want through Europe.

A passport costs 70€ and you have to do the whole bureaucracy for it, take a picture and visit your local town hall. So if I want to visit the UK with my wife, it would cost us 140€ extra and we might have to take time of work to get the passport. The alternative would be, well, every other European country. France. Spain. Italy. Why go to London, when you could also go to Rome oder Paris and it's cheaper?

Also: The UK was of course a popular destination for school trips. All pupils are learning English and therefore it kind of was a natural destination. Visit London. Go to a few museums. Visit that Shakespeare theater. Those trips are impossible now because you'll run into serious problems with pupils without german citizenship.