[forgetfulness]

Everyone got drilled into them in school the stories of scientists and philosophers clinging to outdated models and introducing extraneous elements to extend their life in light of contradicting evidence, the piling up of epicycles to explain celestial movements by circular motions, or luminiferous aether for light to be wave in a fluid medium.

So of course when you first hear "so astronomers found out the equations don't work out with the matter we can detect, so they figured that there must be uhhh... more matter, invisible matter! That exists but you can't detect no matter what!" it sounds like those examples.

If you dig in deeper, then you realize that it's not just fudging of equations and that there being mass that's very sparse and unaccounted-for makes sense.