Some creators have been unhappy over the limited methods through which they can earn a living from YouTube, and many are worried that ads will disappear from their videos even when they've done little wrong. Rivals like Facebook, Instagram (which recently released a longform video app) and others have for years tried to lure away big names, and YouTube has a history of paying up to keep its stars on board.
In a bid to keep creators happy, YouTube has recently added more ways for them to make money, such as a merch program, letting viewers pay to pin comments to the top of a live chat, and making Twitch-style paid memberships more widely available. Paying top names to promote such features could show other creators there are more avenues to earn a living on YouTube than just ads. The features give more ways for YouTube to earn a cut too.
Meanwhile, it seems the company isn't requiring stars to keep their content exclusive to YouTube under the new contracts -- they can post material elsewhere, as long as they upload videos to YouTube first.