Why is the handle of sauce pans tilted and not horizontal?
The answer from the 'Product Manager - Cookware' of Zwilling, translated to English:

[Snipped introduction]
Different factors  influence the design of the handle during the product creation process. At the first step there are optical reasons. This is the phase of the first design drawings.
As soon as we decide internally on a draft, we craft plastic prototypes that are attached to the corresponding pan body to see the size ratio &quot;live&quot; and verify the look and feel. If we feel that one of the two factors is not optimal, we do another design round.
Stability does essentially not play any role for the tilt angle, more decisive are the handle connection and material thickness.

[The last paragraph was likely in reference to my question about having a certain tilt angle for better hanging on a handle. &quot;Better&quot; was interpreted as 'more long lasting'.]

The answer from the 'Consumer Service WMF', translated to English:

[Snipped introduction]
The pan body shapes and the handles are only attributable to the design. As every human has a different taste, we have an assortment of different designs. There is no other technical reason for the handles and shapes of sauce pans.


Summary:
An aesthetically pleasing hanging on a handle is at least not such a concern during the design process at Zwilling that it was mentioned. WMF flat out says it's just design.
If the premise of the question is actually true, that there was indeed a change over time, which is questionable, then at least these days such issues play no longer any role for large companies.