Most GB if you only look at one of their bonuses aren't that great.
Let's test that statement.
Zeus: attack bonus makes it great
Lighthouse: supply bonus makes it great
Aachen: attack bonus makes it great
St. Marks: coin bonus makes it great
Castel del Monte: attack bonus makes it great
Royal Albert Hall: supply bonus makes it great
Chateau: quest bonus makes it great
Alcatraz: unit bonus makes it great
Cape Canaveral: FPs make it great
Arc: contribution bonus makes it great
What about the rest of the GBs?
Babel: not popular
Colosseum: extremely unpopular
Hagia Sophia: mixed reviews
Notre Dame: extremely unpopular
St. Basil: mixed reviews
Deal Castle: mixed reviews
Frauenkirche: not popular (same as Babel)
Capitol: not popular
Space Needle: extremely unpopular
Atomium: mixed reviews
Habitat: mixed reviews
Inno Tower: mixed reviews
Lotus Temple: very unpopular
Dynamic Tower: mixed reviews
Voyager V1: not popular
Rainforest Project: mixed reviews
Observatory: very popular, but only requires 3x3 space
What do the second group of GBs all have in common?
They either: don't help the owner (observatory, atomium)
Or: don't have a single excellent ability (when factoring in size)