Because I grew up in the 1970s. And because I later spent the better part of 20 years living in Chicago, almost all of it spent on the south side. In that part of town there was, among the homegrown population, a sort of perennial groove that was inarguably classic -- definitive. Once winter broke and people came outdoors, you could expect to hear certain spring soundtracking. Roy Ayers Ubiquity and early Kool & the Gang being big favorites. Early-to-mid '70s era Stevie Wonder and maybe the occasional Steely Dan joint. But guaranteed plenty of EW&F.
Earth Wind & Fire having started out as an entity very specific to the Chicago music that it evolved out of. In the group's early years, when its lineup was constantly shifting. In those days its membership encompassed musicians who'd played with local funksters The Pharaohs, as well as others who'd been under the mentorship of AACM multi-instrumentalist and former Sun Ra Arkestrateer Phil Cohran. (As evidence of that latter connection, check the larval EW&F's contributions to the Sweet Sweetbacks's Baadasssss Song OST.) And then once the band's lineup began to finally solidify, in stepped producer & arranger Charles Stepney to help steer them toward the limelight. Charles Stepney himself being a whole 'nother Chicago music story.