Remember when the Oscars had supporting actor categories?
Technically, of course, they still do. But category fraud — manipulating nominations to achieve maximum Oscarage — has changed the supporting races so much that they no longer accomplish what they were created to do: honor the character actors who are the backbone of the movie industry.
Half of this year's 10 supporting nominees are lead actors who landed in the supporting category because it gave them a better shot at winning.
Generally, movie studios decide which categories to place actors in, and the decisions don't always parallel a movie's credits. For instance, Mahershala Ali is a billed-above-the-title co-lead in "The Green Book," and everything about him screams "leading man," but he'll probably win the supporting award (for the second time in three years) because his character has more screen time in which to make an impression than the legitimate supporting actors he opposes. I'd also argue that Adam Driver is a co-lead in "BlacKkKlansman" or, at least, a lead who gained awards traction by taking a supporting part.
The actress category is even less "supporting." Rachel Weisz and Emma Stone, both previous Oscar winners, are co-leads in "The Favourite" with best actress nominee Olivia Colman. Never mind that Stone's role is probably the largest of the three and definitely has the biggest character arc. The producers knew there was no way all three would get best actress nominations, so they pushed Weisz and Stone off to supporting.
Amy Adams' role in "Vice" is not as big as co-star Christian Bale's, but she has the primary female role, she's billed second and it's her character's desires that drive the plot, so if she is "supporting," it would be interesting to know whom she supports.
Studios are out to snag as many Oscar nominations as possible, by any means necessary. The classic recent example of category fraud is 2015's "Carol," in which Rooney Mara was unquestionably the lead (the Cannes Film Festival gave her its best actress prize, in fact). But Focus Features pushed her for a supporting nomination because she was not as well known as co-star Cate Blanchett, who was thought to have a better chance in the lead category. (As it turned out, both went home empty-handed.)
Usually, award givers let studios slide with these shenanigans, but occasionally the gamesmanship is so ridiculous that they balk.