I do not understand how something without any direct evidence whatsoever became lodged in the paradigm of science. Dark matter is not necessary to explain galac

I do not understand how something without any direct evidence whatsoever became lodged in the paradigm of science. Dark matter is not necessary to explain galactic rotation curves.[1] The original observation that spawned the idea of dark matter was of a galaxy's rotation in isolation. But galaxies are not gravitationally isolated. I am unsure about the other stuffed lumped in that dark matter is supposed to explain. But the problem of galactic rotation curves has been elegantly solved without the need for dark matter. [1] https://www.youtube.com/watch?v=PL0ewiwqoTw https://www.youtube.com/watch?v=PL0ewiwqoTw