Nothing remotely as sophisticated or complicated.
Those are Iron Dome interceptors, which have a minimum change of actually successfully intercepting a ballistic missile.
Even the Israelis realise this, which is why the Iron Dome is firing in a spread pattern and in multiple waves. Such firings are essentially performative, with putting up a show being the primary objective instead of expecting to actually hit anything, so in essence isn’t that different from Iraqi or Iranian AAA blasting away wildly into the night sky.
Indeed, if it does transpire later that Iran can still fire much larger waves of missiles but is choosing not to do so in favour of small scale launches, one of the reasons may well be that Iron Dome intercept rates increases the more ballistic missiles you fire, especially at a single or closely packed group of targets. It’s just maths and probability, if the Israelis are just spamming Iron Dome missiles into the air, the more incoming ballistic missiles the more Iron Dome interceptors in the air, and the greater the odds one of the Interceptors comes close enough to a ballistic missile to be able to actually intercept it.
Other factors could also influence Iranian decisions to fire smaller salvos, for example, smaller salvos means fewer launchers, which might significantly reduce the risk of launchers being detected and destroyed by Israeli air power.