Sorry, you didn't give us enough to determine if that was
sarcasm or genuine disbelief.
Had GL been as successful as any of the Thor films it would have
increased the profile of the character in the public consciousness
- outside of fans, who would have gone to see it anyway.
Characters like Batman, Spiderman and Superman are so big, that
even crappy films can't diminish their popularity. Secondary
characters like GL have a lot more work to do to gain widespread
acceptance, and as such, their films have to be good in order to
raise their profile.
Dark Knight took Batman to even greater heights, the first, superb
Iron Man film made the character a huge success.
What did the GL film achieve ?
poor reviews (it's rating about 26% on rotten tomatoes)
financial underperformance (it only just made back what it cost).
If you saw it and liked it, more power to you. However, there are many who felt that it was not a particularly great superhero film.
Myself included, and I like GL, in fact the GL animated series was arguably more fun to watch.
In contrast, GL in the comics has had some terrific stories in recent years,
(rebirth, Sinestro corps war etc), which have raised the character's profile,
and dare I say it, his brand.
As such, the GL film damaged the brand so as to make it tougher to reboot the character. Studios will be less likely to take a risk on a film, and audiences will be less likely to go and see it, as in .....
"Hey, let's go see that new Green lantern movie ."
"Nah, the last one sucked, let's go see fast and furious 12, I hear they
race across the great wall of China, and Vin Diesel talks in an even deeper voice."
There you go. Probably the best proof of the damage GL did is that we
haven't seen a sequel yet ( whereas after Batman Begins, the next two films were in the works in short order, Marvel's films come at an even greater regularity, Amazing Spider-Man 2012, ASM 2 in 2014). GL came out in 2011, and who's talking about the sequel, just a bunch of guys on a superhero forum......like us (and Geoff Johns, bless him), but the execs aren't keen, having not made their money's worth on the first one.