Doc is weird. And people don't want to put time in a character that's similar to another one yet less viable (think Melee Roy).
That being said, you gotta ask yourself: what does Doc have on Mario? Most people say either "nothing" or "killpower." But let's be real.
Doc' OoS options are arguable one of the best of the game. (On the levels of
![Charizard :4charizard: :4charizard:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
and
![Ness :4ness: :4ness:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
). Up B has a meaty disjoint, kills, and comes out extremely fast (frame 3). Usmash is incredible and got buffed with an extra active frame so the hitbox covers his whole body (with his head being invincible). And Bair OoS punishes cross-ups with a powerful 13% killing hitbox that can be SH FF autocanceled. Nair OoS is another option that is good for catching opponents that he couldn't normally reach. So his OoS options are legit.
His edgeguarding is... pretty good. Tornado is active for a while and kills off the sides, which is good. Up B catches a lot of people with that incredibly large hitbox. Bair is good, Nair can gimp, Cape cheese, etc. etc.
But the real reason why Doc is in everyone's bottom 5: his combo game. People expect him to have some kind of Mario-like easy combos (Uair for days -> Bair off a Dthrow or something) but he just doesn't have that. What he has is a Bair that's safe on block, amazing OoS options, good edgeguarding, and improvised combos. I say "improvised" because when playing Doc I dont find myself thinking "If I utilt I can go for a string of Uairs!" like many other characters. I look at what they're doing, read their DI, an figure out what to go for. Off a grab I can Dthrow, Fthrow, Uthrow, whatever just keep em guessing. Jab Jab -> (who knows? You don't. Maybe the up B is coming. Maybe ill shield your frame 1 jab and go for a hard punish. Maybe ill grab. Maybe ill Jab 3. Etc.)
And that kind of playstyle requires you to become Ganon and not fight the character, but fight the
player. Which is exactly the reason why he's bad.
And also the reason why he's my secondary.