I agree with you, thinking back I can't quite recall why Ollie was dropped from the main Justice League team. But look at the line-up of it these last five years and it has been an inflexible one - newcomers like Element Woman go the way Ollie did, others are there purely to serve a given plot, and the arrival of other independent JL teams like the European branch and JLDark seem to have an uncomfortable air of illegality about them. Unsanctioned and unwanted by the main League line-up.
Green Arrow as a character really does need better defining, but his relationship to the rest of the superhero community in particular is an unexplored one that urgently demands some exploration, along with Black Canary's.
The way I see it, as the Justice League title goes on, I think the roster should be:
AquamanBatmanCyborgFlashGreen ArrowGreen Lantern (Baz)Green Lantern (Cruz)SupermanWonder Woman
To my friends in DC, ADD GREEN ARROW TO THE JUSTICE LEAGUE DURING REBIRTH!!!