1. Why has WN virtually had 0 addition/expansion at DTW in the last 3 years while markets of similar or smaller size continue to gain from WN?
WN just barely set a record for enplanements in 2016; the 845,604 passengers who boarded WN's jets was exactly 81 more than in 2007, when a combined 845,523 travelers traveled WN & FL. Unfortunately, WN is running behind its 2017 pace and given stagnant capacity the remainder of the year coupled with the seasonal suspension of LAS, it's not likely they'll surpass last year's coupe.
Historically, WN has had limited success in Detroit. 30 years ago, they choose DET to be their Midwestern gateway, envisioning it would have the same impact for them that MDW had for Midway Airlines. Detroit failed to deliver its promise to develop DET, Midway went bust and WN established a mammoth hub at a re-built MDW. Things couldn't have worked out better for them, especially given the direction SE Michigan's economy took during this timeframe.
WN (and DTW) was gate restained at DTW in the 1990s, so it paid for (but was reimburse via PFC) the expansion of Concourse A, which opened in 1998. Enplanements immediately grew by 15%, but growth stalled and by 2003 (following 9-11), WN shrunk to its smallest position at DTW since the mid-1990s. WN embarked on an ill-fated expansion at DTW in 2007 (including the MCO service, discussed extensively in previous installments) but regressed to its late 1980s/early 1990s form shortly thereafter.
It's pretty telling that in 2007, WN + FL was a larger carrier (606,133 enplanements for WN + 239,410 for FL = 845,543 total) at DTW than it will be ten years later, in 2017. Meanwhile, WN is on pace to enplane more than 1,1M passengers at MSP, a market they did not serve a decade ago.
Reality is, DTW is a market that just hasn't worked out for WN. This is largely because the local business community has never embraced WN* (e.g. GM's memos from when it was pumping money into ProAir) whereas NK long served the markets leisure travelers flew to most, at prices WN couldn't match.
*I'm guilty of this. Either me or one of my co-workers travels to Chicago weekly; these are day trips to a satellite office on the loop. (A) The North Terminal is more convenient than the McNamara Terminal, since our parking contract is with a vendor off Merriman Road; additionally, it's significantly faster to navigate the North Terminal -- including the process of getting to security, walking to the gate & often landing / taxing (one of my biggest pet peeves is arriving on DL after midnight on the runway in the middle of nowhere, spending 20 minutes taxing to the far ends of the terminal and having to hoof it since the tram's down for the night); (B) Midway is more convenient than O'Hare to navigate and get to our destination in the Loop; (C) WN offers a superior onboard product to DL and UA on this route - even on a fully loaded 738, everybody receives a drink and peanuts. Meanwhile, the flight's too short for Main Cabin service even on a DL CR7 and often FA are too lazy to serve even F or C+. UA tends to be hit-or-miss -- sometimes full beverage service, sometimes just water service, sometimes no service. And yet I rarely, rarely, rarely fly WN...
2. Why hasn't G4 gone to DTW yet? Will they?
DTW isn't the type of market G4 seeks out; there's too much ULCC competition. G4 does serve Metro Detroit via FNT & TOL.
If you are an American who drives an auto built by a foreign-owned company yet complains about your favorite airline buying Airbus, then you are nothing more than a whiny hypocrite.