Why Did JLI Succeed When Justice League Detroit Failed?
The early 80's weren't a great time for the Justice League of America saleswise, so the decision was made to give a new spin on the Justice League concept. The heavy hitters were sacrificed in favor of preexisting c-listers (Vixen and Steel) and outright original characters (Vibe and Gypsy). There were remnants of the original Justice League still in tact such as Zatanna, Elongated Man, and Martian Manhunter, but they were never the League's most popular members.
Famously, the new Justice League that had started with JLofA Annual 2 was even more ill received than the Justice League stories that preceded them. Amidst the Legends crossover, the 'Detroit' era of the Justice League ended with issue 261.
Soon afterwored the Justice League title was relaunched with a new #1 under the helm of Keith Giffen, J.M Dematteis and Kevin Maguire. This more humerous Justice League ended the franchise's streak of misfortune as it became a huge hit, becoming one of DC's top selling titles and for the first time made the Justice League a family of titles, spinning off to Justice League Europe, Justice League Quarterly, Justice League Task Force, and Extreme Justice.
This has always perplexed me because the JLI had much more in common with Justice League Detroit than you might think: Both Justice Leagues tackled smaller scale threats than the Justice League of the Silver Age and Bronze Age, and both favored lesser known characters in favor of B-listers and C-listers. Sure JLI had Batman, but so did Justice League Detroit in it's latter half.