What the hell happened?

I've been playing just fine for the past few months. No flamers or intentional feeders. At most the unfortunate unskilled player. Then the new ranked season happens and all hell breaks loose.

We were winning in both kills and objectives before this went down. It was my first placement game.

I had a top laner who decided to feed when they decided no one deserved to win. Just started running out there to the death.

Our adc started doing the same after our support was aaing the minions. She said she'd stop if he apologized but they both started flaming at each other.

The support eventually just went back to base and stopped playing. Just yelling at the adc.

The jungler who had been arguing with the top laner since the beginning stopped right at the end too.

I didn't even know what to do. Why did this happen? Is it the new seasons fault? What about the ranked season brings the hate out of people?