Q: Why do you think are there so few songs in 9/8, when 3/4 is so ubiquitous?
A: you might be implying that it ought to be more common to see 9 like 3x3. usually when that happens, it tends to be fast enough that 3/4 is more reasonable to put on the page. there are many songs that indeed are slow 3/4 with each beat divided into 3. but people are probably scared to put 9/8 on the page because a lot of people wouldn't know how to handle it