Is it, though? For one thing, many feel that projects like Dataland led directly to the modern Windowed User Interface. One can think of opening windows as a kind of limited zooming with very specific affordances. The iOS UI is cited in the Wikipedia article on ZUI as being another example.

Basically, any UI in which one can "drill down" into greater detail or smaller/more specific contexts is effectively a kind of zooming. The problem, is losing the connection to the larger context.

Another thing to consider: At the time many of these things were tried out, there wasn't enough capability in the CPU and UI to render complex data fast enough. In fact, I was involved with a round-trip UML DB to UI product dating from the 1990's, which looked great in demos. However, it became dog slow when actually given someone's company database. This was a problem which dogged many projects with innovative UI ideas. (A problem which many CAD software apps deal with, and which seem to have been solved to some degree.)

semantics in 2D isn't something that's easy to grasp cognitively unless you specifically arranged things that way

Do you have specific examples?