Of course, the bank has an interest in security. That customers want to save the notary / registration costs for a land charge is somehow not surprising, but it certainly doesn’t impress a bank in the long run. Real estate loans are long-term borrowings. No one can know what the situation will look like a few years later (illness / disability / divorce / death ...). Therefore, the bank also wants to be prepared for such events and not end up looking foolish and receiving money only with great effort.
At the same time, the lending guidelines of most banks provide for security through a land charge. The caseworkers naturally adhere to this. Of course, it is also possible to pledge account balances.
Another argument is that banks only have to reserve little equity for very secure loan granting. They can thus issue comparatively more loans with the same equity, thereby optimizing their return. Within the framework of the Solvency Regulation, there are different securities for the various approaches, which can be taken into account in a way that reduces equity. These include, especially, land charges.
I will definitely keep my fingers crossed for your negotiation adventure. It’s sure to be fun.