has been historically mocked and thought of as awful for a couple simple reasons. he had some huge nerfs that naturally, people overreacted to as they always do, screaming that he was made worthless. he also has a severe identity crisis, with his "established" lane being bottom, despite him functioning much better in solo lanes. it goes something like this
i think urgot is bad > i rage, flame, or AFK whenever there is an urgot on my team > constant raging, flaming, and AFKs every game cause urgots winrate to plummet > i see that urgot has an incredibly poor winrate, which reaffirms my belief that urgot is bad > repeat endlessly
he's been in a poor circumstance for a long time, and not everyone is letting go of their long-held beliefs about him. he's slowly climbing out of that hole now, due to getting a (very minor) buff and seeing some pro play, causing people to believe that this buff saved him, and somewhat accepting him as a pick, rather than automatically classifying him as a troll pick.