............which being ruined by greed and ignorance.

why is it correct? why shouldn't be " greedy & ignorance"?
"ruined by" must be followed by a noun (or noun phrase). "greed" is a noun; "greedy" is an adjective.

Note that "ruined by greedy ignorance" is possible because "greedy ignorance" is a noun phrase, consisting of adjective + noun. However, "ruined by greedy and ignorance" does not work because it means "ruined by greedy and ruined by ignorance", and "ruined by greedy" is ungrammatical.
Mr Wordy explained beautifully.And I can say it in another way.

1-By is a preposition so it is followed by a noun,gerund or noun phrase like:

A:....which being ruined by greed and ignorance

B:.....which being ruined by being greedy and ignorant.

C:......which being ruined by greedy ignorance. (as Mr wordy pointed)

2-Meanwhile"AND" combines two nouns,adjectives,verbs, or adverbs:
A: She is tall and thin.(adjectives)
B:She speaks slowly and carefully.(adverbs)
C:I Play and study lonely.(verbs)
D:Does he notice his ignorance and stupidity?(nouns)