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.
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.