Detroit's rap scene never took off because the midwest in general has a weird issue in falling victim to being not beholden to a broader sense of regionalism; they're not in the deep south, nor are they East Coast. You see this in Ohio groups like Dayton Family or Bone Thugs where they're a hybrid of Memphis style stuff and West Coast stuff, but obviously nobody from Memphis or California will necessarily agree with them being 'theirs' (Bone Thugs got by with Eazy adopting them and giving them a cosign obviously and by that point they really ramped up the Cali-isms).
Don't also forget that whereas the east coast, south and west coast eventually abandoned electro for rap, the midwest KEPT electro alive via acid-house, techno and whatever. That split musically doesn't happen nearly as much in LA or NYC because while dance music culture had some footholds there, the rap culture was cultivated and attracted a lot of major label attention; Motown had moved its base of operations out of Detroit before the genesis of hip-hop and with that one of the biggest black labels of america had no eyes there. You had indies certainly who were able to garner attention but few of them got a lot of access to national distribution, few of them got attention in The Source or whatever. This is why Esham who is undoubtedly one of the most innovatory rappers stylistically, lyrically... He just never got the exposure! Eminem got on Interscope, he got to be that guy. Major Label Attention or Indies with Major distribution and one or two crossover acts (2 Live Crew become a national news item; Three Six Mafia jump to Priority early in their career; Geto Boys get attention and endorsements from Rick Rubin, No Limit were at first a Bay Area/California label and got to learn the midwest/south/california distribution network mapped by labels like Sic-Wid-It BEFORE moving to New Orleans to dominate that market) is what allows a regional scene to break through beyond their zone.
Dilla's Detroit was essentially based around a bunch of guys who angled themselves after East Coast acts, but there were Detroit rappers who modeled themselves after West Coast acts or Southern acts. MC Breed did the song with Tupac after all; Kid Rock, before the country reinvention was overtly indebted to the real version of Sir Mix-A-Lot from "Posse on Broadway". But OF COURSE the East Coast aspiring rappers always get groomed for success even when they're 8th tier boring backpacker rappers. Hell, the main reason we know about Dilla's Detroit is frankly Dilla went to Q-Tip as an indentured servant for x years and by doing work for the established industry/NYC acts, he THEN was able to get himself and Slum Village major label deals.
Chicago was like this for a long time too, because you have a East Coast centric fave like Common but then acts who lean to southern aesthetics like Do Or Die, Twista, Psychoward, Crucial Conflict... Some of whom were on Major Labels, had big hits in their areas, but couldn't transcend the needs of an industry that was so entrenched in East Coast standards and expectations. Kanye got the chance to grant a lot of his attention back onto Twista and Common. Keef being groomed as a new Next Big Thing on the internet allowed Durk, Reese and King Louie and the industry at large recognized that when... From the internet wise, Lil B and from the greater sort of hype machine, Kanye all cosigned Chief Keef. Now however we have a consistent pre-existing pipeline of rappers from the Chicago area being granted attention in the broader music industry. Who does that for Detroit? Eminem? He only put on his friends (Royce, D12, Obie) Big Sean? Big Sean hasn't put ANYONE ON (I imagine because he's so devoid of personality he can't have friends.)