I think memories are best formed from coherent associations put in a meaningful context, and that these extraordinary states of consciousness lend themselves extremely poorly for any of those requisites of proper and long-term remembrance.
Seems very hard to say: I don't know how delusional nitrous oxide insights are, whether they make sense merely by the virtue of lacking proper critical thinking... or whether there is something to them - don't know about the key to life, but at least by Earth standards... and just impossible to put into context or connect to any sober frame of reference. The mystical frame of reference just doesn't have much at all to do with that.
Dissociatives or GABA modulators messing with cognition or memory surely won't help, but maybe I would also not expect any coherent thought to form when so impaired... and serotonergic psychedelics can still pose these problems while having no clear pharmacological reason to impair cognition or memory, and also some of these profound experiences don't at least *feel* so out of it. I know that feeling of just being blurred into fucking oblivion. The feels say something not way off, but the thoughts say hardly anything at all.
Another possibility is perhaps that something goes wrong with carrying short-term memory into long-term memory. Possibly that doesn't take full-on disruption of cognition and memory but just a disruption of coherence of this kind of processing which is different from memory formation an sich.