The German brands are much better quality and nicer places to sit and drive nicer than most others and arguably look nicer, with them only becoming marginally affordable via PCP and lease plans however it has made them even more accessible than likely at any other point.
The company car / capital gains tax is what has really driven the increase, previously businesses were buying up bucket loads of mondeos and vectras, they were built for a price point, hence the Mondeo man acronym, then due to the tax people didn't want company cars and if they did they wanted decent ones to justify the cost.
Those that opt out of having a company car, due to finance as mentioned, those that would have been given a Mondeo can now choose what car they want, it is little wonder they choose one of the German brands, the German brands do come out on top of almost all head to head tests.
That said German reliability is a thing of distant memory I don't believe they are any more reliable than most others brands
there is the badge snobbery that if you own one your somewhat superior or less poor, you wouldn't get a deano driving round in a Mondeo or insignia etc.
Having driven new Korean varieties when my car has gone in for work on many occasions this past year I can confidently say that the German or other car Considered prestige like a lexus, Jag Alfa, are much nicer places to be.
Yes the Korean is cheaper, and most instances relatively stylish, but there is a reason they are cheaper, corners have been cut in areas, and compared to my 20 year old Audi A4 I've not been convinced it's worthwhile replacing, other than for another Audi or car of similar ilk.