Probably because
and
are terrible mids, because they are splitpushers and that has no place for midlane.
A) Some mid laners can and do split-push. It's not banned. (hi
!)
Not to mention your team doesn't need another tank or bruiser when you probably have one in the top/jung/or support.
B) Again, I don't want to suprise you. But. You don't always have a tank in those other positions. (Hi
,
and
!) And sometimes, even mages build tanky. (Hi
!)
Your team needs an APC in the midlane, because your team otherwise is lacking that damage for teamfights.
C) Both Shen and Shyvana do mixed damage. Shyvana does a lot more. So you're not losing magic damage. Not only that, but magic damage can come from other sources. (Hi
,
,
!)
Normally, I just make the joke and let it collect downvotes. (I actually do run them mid, but I also run others.) But you're post just screams "sheep". Just because the meta favors 1 style of comp and set-up, that doesn't mean others can't work. Change, thought, and calculated risk are how the meta evolves.
It's the reason we don't still have ADC's mid with tank+support bot and APC top. It's the reason we no longer favor roaming supports (I see you, Bard). It's the reason we recently made the shift from an "assassin meta" to a "tank meta".