because unlike ADC , which ha seen dominated exclusively by marksman since forever, Support, like jungler, has never been a role dictated and dedicated by a singular set of classes.
Its mostly due to what they fulfill.
Support and Jungle are mostly ambiguous because they exist out of a need to properly allocate resources moreso than optimizing class to position like Mid/ Bot and Top.
Junglers was to free up a lane (top lane) so they could benefit from solo lane farm and EXP while the jungle mobs could actually be properly taken advantage of, while support was mostly just due to having to put the 5th player somewhere and being with the vulnerable ADC who wasn't as level dependent as other classes was deemed the best, and thus the 5th persons role became centered around 2 things. Protecting the ADC and being given the chores no one else wanted to do but someone HAD to do.
In this regard, Support is a role that is almost fundamentally shitty, because it is conceptually designed to be the shitty end of the stick, as it exists moreso out of having to scrounge with what you have and being given the jobs no one else wants to do so they can properly optimise what they need to do.
Back in the day, this meant warding. And Im not kidding when i say that your inventory looked like :

But i digress, i went off on a tangent there.
The point is, support choice doesn't get scrutinized as much because support isn't dominated by a class because support exists moreso as a means of filling the fifth slot moreso than anythign else.