The whole not using the jetway thing in Germany blows my mind. I flew Lufthansa SEA-FRA in 2019, and the fully packed 747 had to walk onto the ramp, and load up into buses to get to the terminal. Outrageous. The only time I've ever done that in NA is flying at places like CAK in a micro regional jet.
LCCs generally do this because charges for the apron are cheaper than the jetway.
With Lufthansa, I'd assume that FRA is super busy and didn't actually have a gate available at the time; a 747 is a really large aircraft to load using buses.
Apron buses are very common in large airports and I always found it really efficient. From memory I’ve used them at Haneda, Narita and KL. Perhaps the ones in Germany are just altered metro buses though, which would be terrible. Apron buses are efficient due to being low to the ground, having very wide doors to accomodate quick loading and unloading, typically no seats.
They may be efficient given the layout of the airport (which can't be changed), but if you are to design a new airport, you cannot beat the efficiency of jetways. Hundreds of people just walking down the hallway.
European low-cost airlines are terrible. They do everything they can to lower the fees they pay. That often involves skipping major airports, unless they can negotiate a cheap enough deal with the airport. Those deals tend to involve things that make the passenger experience worse, because the airports don't want normal airlines to choose the same deal.
If you choose a normal airline and fly to any reasonably big airport that's not overcrowded, you'll get a jetway outside exceptional situations.
A decent new airport or significant airport reconstruction costs probably $5B+ (DEN cost $4.8B in the 90s; Beijing Daxing cost $11.5B) In austerity-minded Europe there really isn’t money for this. Even if there was, NIMBYs and green campaigners mean there is very little appetite to pursue it politically.
