That the exact location of where rockets land was always treated as sensitive information everywhere to make it hard for the other side to adjust their targeting? During WW2 the British government went as far as coordinate fake news about where the V2 rockets landed with the media to make it harder for the Germans to hit anything.
A major difference here is that during WW2 the rockets were unguided and fully relied on fuel-weight calculations. These ballistic missiles are GPS guided and don't suffer from all of the unknown factors.
There is certainly a case to be made for secrecy, though it's more likely they don't want to let Iran know whether F35's, tanks or other military equipment were hit. Israel already claimed they "intercepted the majority of projectiles" but the videos don't really corroborate that. Similar to the Hamas "limited ground operation" last year israel tries to hide all evidence and then crafts their own story of what happened.
They most certainly can be guided. Ballistic means that the terminal phase of flight is not propelled, eg they are just falling and no longer accelerating.
Guidance can be inertial, magnetic, radar, GPS, or even star-map for ICBMs, or a combination of many of these. Minuteman missiles still rely on the position of some stars to orient themselves in exosphere coast phase. Part of their flight may be unguided, namely 3rd stage ascent where they are spin-stabilized, and during reentry phase where atmospheric plasma makes GPS guidance impossible and inertial might be inaccurate.
Because it's feedback on how effective their targeting has been when confronted with whatever electronic warfare and misdirection Israel was using to defend themselves.
That sort of information might let the attacker make adjustments to be more accurate next time
If it was because of GPS jamming the next shot will also miss, but differently. They don't just always jam everything 500m to the east. These are guided missiles which adjust their course and even performed zig-zag dodging maneuvers on iron dome interceptors.