The most inutitive purpose of illustration is to communicate some sense or idea, or perhaps a set of facts, or occassionally to express some bold aesthetic style.

Those purposes aren't obviously served by rendering the exact detail of a 2D projection with accurate scale and perspective. Doing so can be an impressive technical feat, or a prevailing style (as it became for a while), but can also be seen as a somewhat stubborn rejection of visual language and editorial expression.

Techniques for realism and perspective are evidenced throughout history, but even now you can see it rejected in plenty of both commercial and fine art because it's just not that important/relevant most of the time.

It’s weird to think of it as such, but perspective drawing really is a technology that most artists did not have access to for most of history.

I’m super not an art historian, but I think the Renaissance era is when you really start seeing 3D perspective in 2D art.

In some artistic traditions, visual style has been "conceptual" rather than "perceptual", meaning that objects are presented to emphasize their meaning rather than how they might naturally look in a scene. The two such artistic cultures you are most likely familiar with would be Medieval Europe and Ancient Egypt.