My wild ass guess: prices dropped, causing battery packs to get bigger and increase availability to people who may not understand or care about the risk. Additionally, with lower base cost of lithium ion batteries, you get more cheap crap that is not engineered well.
I think the proliferation of power banks is also relevant. More and more people have come to consider a power bank + cable to be normal travel gear. High energy density (it's not surrounded by equipment meant to be powered from the battery) and people often cheap out figuring the cost of a bad one being low.
