Some go through - a very small minority. One hit a pipeline, for example (it's still burning). Another a car. A few Israeli casualties thus far (far far less than Palestinian ones of course). But then again it's easy enough to produce hundreds of the things - it's basically a steel cylinder with a solid sugar + fertilizer propulsion block at the bottom; and a TNT or fertilizer payload with a fuse that's basically a nail and a bullet. The estimated cost for each is at most ~800$, potentially much less. Meanwhile one iron dome missile costs like 40000$.

And also, even if they don't hit they can have an impact disruption-wise: they had to close Ben Gurion airport because of them a few hours ago, for example. And right now there are large measures in the whole of Israel (schools closed, working only from shelters, etc.).

To add to my earlier answer, here is a close-up footage of a mass launch from Gaza. They're shooting as many as possible at the same time, presumably to try and overwhelm the iron dome. Here is a vid of a successful hit.

Edit: wrong, the first vid is from a Turkish February launch. The second appears to be legit though. Thanks @all_or_nothing for the debunk.