The change to larger tiles is entirely down to a growing majority of people watching Youtube on phones and tablets, so they need those larger tiles to actually see and tap on the video thumbnails on the smaller screens. Personally I think they should at least give the user the option to decide how many tiles per row are on the screen, but we all know Google doesn't do that "user choice" thing.
Though it does also have a smaller side benefit of making it more difficult for slop channels to create a deceptive AI-genrated thumbnail that doesn't actually represent the video's content and is designed for clickbait, which that would be harder to notice at small resolutions.