Why? because not all plants have dmt, first of all. Even the ones that do dont necessarily have it in reasonable amounts to be worth it to extract, and others might have other unwanted toxic alkaloids, or impurities that are harder to clean. But yes there are other plants appart from mimosa which can be used to extract dmt, like some (but not all) Acacias, as well as potentially certain phalaris strains , plus of course chaliponga, and depending if its a high alkaloid one, also chacruna. Maybe certain virola resins could yield good amounts of DMT. Check our WIKI for more information on DMT containing plants, but remember that if the exact % isnt quoted, it might be only very small amounts.