I don’t know what triggers OneDrive advertisements in Explorer. I don’t know if they appear in Windows 10 stable builds or just Insider Previews as a taste of things to come. I don’t know that I even care any more.
But come on.
Nobody in Redmond thought, “Gosh, that’s a little distasteful”? I mean, “Let’s just turn our operating system into a billboard!” offends nobody?