Because in the wild it makes no difference - the true strains will continue as well as the cross-bred ones. In an artificial environment such as the aquarium hobby, "true strains" end up being lost because of cross breeding - especially with fish that are rare and difficult to import. This is further exacerbated by people (and again Im not saying you will) not saying what things are. They end up as mixed strains but still described in the name of the true one. Eventually you lose the original and end up with something else. There are purists who dont want that to happen.
Having said that, as a hobbyist, if you are happy with having paid for a pair of L018's and not actually got what you paid for, and you are happy to breed them for people who could care less if they are true L018s or not, then all well and good. Just as long as you dont sell any offspring as L018s I am sure you will get some pretty fish either way.