Short version
1974 time, Fleetwood Mac were in disarray after the firing of the whole band by their manager Clive Davies. Mick Fleetwood had bills to pay, so decided to reform FM around himself and Christine McVie. He enlisted Elmer Gantry (vocals, ex Elmer Gantry's Velvet Opera, check THEM out when you have a mo) and Kirby Gregory (geetar, ex Curved Air) to join the band. Dates were booked throughout the US both headlining and supporting Deep Purple. Problem was, Christine McVie refused to join, Mick Fleetwood lost his bottle and Gantry and Gregory were left to soldier on as Fleetwood Mac with whatever musicians they could drag in. Word got out that it wasn't 'the real' Fleetwood Mac, venues cancelled, those that didn't suffered riots, law suits flew in all directions and Gantry and Gregory flew home to UK with their tails between their legs. They liked playing together though, so formed STRETCH, a blues band similar to Peter Green era Fleetwood Mac, recorded a blues album 'Elastique' which contained one non-blues cut, the hyper-funky 'Why Did You do It', written by the pair as a dig at Fleetwood and Davis. Against the odds, WDYDI became a big hit, and over the years (mainly through a lot of reworkings/samplings of the song in dance/disco/funk genres) has I guess provided a nice little revenue stream for the pair as a softener for the embarrassment of the Fleetwood Mac Debacle.
Huh, I could have told you that if I hadn't been in a meeting. A chance for the 3rd case of beer gone. Fleetwood Mac never recovered in my view and in recruiting Buckingham Nicks a bit later became a travesty of a band, producing a string of bland MOR crap that sold in millions and made them a fortune. Pah.
Probably quite a few things! Perhaps the fact that "Mac" wasnt in the first line up despite the band bearing his name? Perhaps because they were not called Fleetwood Mac but had "Peter Green's....." added to the front of the name?
Its maybe a good thing that when the residue of the real Fleetwood Mac merged with Buckingham Nicks, they did not take on the enjoined name of Stevie Mac, otherwise they would have had one good album then broken up in disarray with talks of Nicks joining Dire Straits. Then reformed a year or so later for another cameo album that flopped despite a good first track, and broke up again.
Dream on Andy.