It’s a cheap plot device to give us a reason to care about anakin because of what he represents, rather than by who he is. Who he is and how he acts should be what our focus is on, not on a special kind of of bacteria that he has a lot of that means he’s the figure of some prophecy or whatever. Basically what midichlorians do is TELL us we should care about anakin, rather than SHOWING us we should.
It’s cheap, like jump scares and fart jokes.