The community overreacts to off-meta picks because sheeple is a real thing. Humans are social creatures, we're prone to hive mind. Otherwise, some off-meta picks are bad. Some are so unexpected that even if they do well, people don't understand how it could work.
Riot nerfs off-roles because, sometimes, they end up cancer. A good example is AP Yi. A long time ago, before his rework, AP Yi was considered mostly a troll build done in Dominion. Then it rose to prominence in competitive, because he has a 1.0 AP ratio on his Alpha Strike with I believe around 300 base damage, and a /5.0/ AP ratio on his heal.
So basically, he'd press Q, it'd bounce to you (because the bounce range was MUCH higher than it is presently), and you'd lose 1/3 of your max HP. And his CDs reset if he got a kill, so all he had to do was go into a teamfight, Q, Zhonya's/W, Q, and then he turned into a point-click literally unavoidable Katarina.
They didn't nerf AP Yi out of existence because he was off-meta. They did it because it was bullshit.
Solo-lane Lulu is an abomination. Because she is a support, she has the utility to win lanes. When she is alone, this cannot be counter-balanced with the enemy support, and instead, you end up spending the vast majority of the lane phase being kited, nuked, hard CC'd, and then she shields when you attempt to trade with her. And then she proceeds to all-in and kill you repeatedly if you fall behind. And, again, it's virtually impossible for you to NOT fall behind.
At least, when solo-lane Lulu is any good.