as to why... german renter/lessee culture prefers having their own stuff to give it a more homey feel, i guess.
It hugely sucks because things like fridges and stoves often need to fit the dedicated space in a kitchen exactly. The chances that your previous apartment and new apartment fit the same size appliances is virtually nil.
This is why it makes sense for them to just be part of the apartment.
I don't know what you mean by "mistreatment" -- anything in an apartment can be mistreated I suppose, it's not specific to appliances. If you damage anything, that comes out of your deposit. But I'm not really sure what there is specifically to damage about fridges and stoves? They get dirty and you can clean them. They don't generally require any super-special treatment.
But the point is: yeah, "immovable".
The landlord is fully aware that when the tenant eventually moves out, the landlord can require the tenant to take the kitchen with them — after all, it is the tenant’s property, not the landlord’s. The landlord can therefore demand that the outgoing tenant removes the kitchen. This again puts the tenant under pressure, because fully fitted kitchens very rarely fit into a new apartment.
At that point, the landlord can make an offer to buy the kitchen back from the departing tenant so that it can remain in place — but the purchase price is then only a fraction of what the tenant originally had to pay the landlord when moving in. In this way, the landlord can indirectly force one tenant after another to buy the kitchen and later sell it back.
What blew me away was being forced to remove the ceiling lights, and leaving the live wires dangling down. Don't underestimate the difficulty of doing this for someone who has to do it after working hours. You switch off the power of course, which leaves you in total darkness. Naturally I had not thought of that little complication beforehand.