Now, this is an important observation, but it needs one caveat - "fittest for its environment" != "fittest for the stated purpose". I.e. an objectively better tool may lose to a tool that's barely good enough, but e.g. provides a better CYA for managers, in a self-reinforcing loop of popularity.
That's the essence of Worse is Better - shit that's barely good enough will outcompete proper solutions.
(For many, that essay seems to be an ideal to follow; for me personally, it's just the description of the sad state of reality that we need to learn to work around.)
Now hold on. The most successful sprog of nature is humanity[citation needed] and we're a case study in the fact that raw intelligence is more effective than fitness for any particular niche. So: as in nature, there may be a bunch of niche languages, but in time they'll find themselves with a conservation status while a smart language rules the earth.