Also just a guess: We don't have official router freedom in Switzerland, so it may well be that people get an AVM box only to find that their provider only allows their own boxes.

Then there is the confusion that with the fibre-optic boxes AVM markets different equipment variants, sometimes GPON and AON modules are included, sometimes only one of the two. Still others only come with an XGS-PON module, which for a while was not / hardly available on the free market. The risk that customers accidentally order the wrong model and then return the box because the wrong module was included is also higher.

Unfortunately, I cannot answer this question, as my FRITZ!Box has been working without any problems since it was installed last year.