The reason that I suspect that much of the "L" out there is actually LSM is the fact that it is easier to synthesize than the 6-alkyl analogues, being a one-shot synthesis from lysergamide or lysergic acid and the fact that its short duration (4-6 hours) closely matches much of the "L" out there (LSD proper is supposed to have an 8 hour duration). Also of note is the fact that the compound diethylamine is Schedule I / Class A whereas morpholine is not. Hence while LSM is illegal in the US, the precursors might be less suspicious and thus friendlier to someone looking to avoid the psychotically draconian life-sentence for synthesis of LSD proper.