I build web apps as a job and the impression I get is that everyone wants Material, "because" - but I don't know if anyone wants it other than "because" it's the buzzword of the day.
And it always sucks because the clients always say, "Follow Material guidelines BUT make this smaller, make this less round, use this font we paid for, make the buttons different, and also customize all these components".
The guidelines are a culmination of well-researched UX basics in practice. They're meant to be stylistically customizable to any brand, or user preference. It's just the best starting point in software design at the moment.
Sometimes I wonder if the reason is because Mozilla doesn't want to associate their browser with Google. It's just kind of a wild guess, but that's kind of what I think. But then again, Mozilla has some really weird branding fetish