There's a theory that DMT (5-MeO-DMT) might exist in nearly all plants, just in small amounts. Psilocin is 4-HO-DMT, so it's not toofar away in a molecular sense. I'm assuming that tobacco must be easier to genetically alter, or we're just more used to it. One of the early genetic lab exercises was splicing a gene into tobacco plants from fireflies (or something that glows), to make the roots glow in the dark.