The actual answer is that now, more than ever, people are actually getting writing credits for their contributions to these songs.
There's countless stories of some older musician saying they came up with the catchiest part of a song while they were fukking around in the studio, or just in passing, and all they have to show for it is a story that some people may or may not actually believe. Now, even if it's a case of using some premade stems that are deliberately made to just be fillers or beds, or something you saw online that inspired you, it's a whole lot easier to just credit twenty-some writers that it is to try to just let some shyt ride like you used to.
And that's before even getting into properly crediting acts that were sampled.