Being able to do everything with SVGs is admittedly nice. But if Google was worried about performance on small screens and in low-bandwidth contexts, we wouldn't have Material design, as it's animations have quite a bloated effect on performance. Particularly on devices with low power/low processing. Page loads on desktops for some Google sites are up to ten seconds now.
But yes, most redesigns are done just for the heck of it. I have a pretty uncharitable opinion of design and designers too, if only because very few Silicon Valley designers seem to have any idea how the users experience (and hate) their work. (I remember back when I heard about Google doing heavy testing with normal users before making changes, and it's very clear that that stopped when Duarte stepped in.)