I'll take a stab at this based on the comments.
"Bad" resource requests tend to be excessively subjective. See, for example, this question, which gives some examples of purely opinion-based resource requests ("if I like Jane Austen, who else might I like?"). Purely opinion-based questions are off topic everywhere on the Stack Exchange network.
Most importantly, Stack Exchange strives to be a repository of knowledge (not just a forum for discussion or sharing opinions), so good answers should include specific factual or textual evidence. Good questions should be able to be answered in a way that can be factually justified (rather than just soliciting opinions). They should also be useful for future readers.
For example, this question on Biology SE is an acceptable resource request because it can be answered in a factual way and is potentially useful for future readers.
"Bad" resource requests tend to attract opinionated answers and spam, and answers can't necessarily be justified in a factual way. Resource requests that are highly localized to your specific situation are also off-topic because they're not likely to be useful to other readers.