Why is there so much true damage in the game right now?

Ever since the post-death damage report update launched I've noticed that a hugely surprising amount of the graph nearly every death is white for true damage. I've played since season 2 and true damage sources when I learned the game were few and far between, except Irelia/Olaf/Vayne/Ignite, and were considered extremely strong and hard to itemize against. So yeah pretty much just the title, why over time has there been so many true damage sources added and doesn't that much true damage floating around really hamper the ability of defensive items to do their job?