Rules of the universe
In this universe (which yes is related to the one in this question), a species has achieved faster-than-light travel with some caveats. A ship with a warp drive, a device that uses microwave-generated plasma to deform spacetime around the ship, can be used to generate an Alcubierre-style warp field that can allow for faster-than-light travel. On smaller scales, weaker warp drives can also generate artificial gravitational effects, allowing someone sufficiently capable to use artificial gravity to make "magic" and levitate objects, throw things across rooms, etc.
The caveat is that performing the calculations necessary to actually tell a warp drive what to do to produce a given effect is extremely difficult, and the species that has access to the warp drive technology doesn't yet have sufficiently advanced computers that would allow them to do the calculations there. So in order to travel across the stars, one must spend a long time calculating exactly what parameters must be input to the warp drive in order for the drive to take them to their destination instead of collapsing the ship into a black hole (which happens frequently in this universe).
One thing that can be done with the warp field without much calculation is a geonic communicator, a device that generates geons (essentially self-contained gravitational waves) wrapped around alpha particles so that the geon has built into it a warp field that carries the alpha particle forward at an exponentially-accelerating speed, eventually exceeding the speed of light. The time it takes for a geonic communicator to send a message increases logarithmically with increasing distance as opposed to linearly for normal light-based communications; these are high-energy devices and usually require large electric generators to power, but they allow the conveyance of information across space faster-than-light so that interstellar colonies can effectively communicate with each other.
Minor notes: warp drives are considered expensive but not unobtainable; a small single-person orbital ship might cost around \$100,000 equivalent, and the warp drive to go with it might bring the total cost to \$250,000 equivalent. Geonic communicators are very expensive devices, usually government-owned, that cost upwards of \$300,000 equivalent per communicator and require about 10 kW of power and an alpha-particle source (like a brick of americium) in order to transmit or receive messages, which cap out at a bandwidth of around 1 MB/s. Additionally, if a warp drive is improperly used, it collapses the ship's mass into a black hole.
The issue that I'm having
The species with access to FTL isn't a peaceful one - in fact, wars post-FTL happen frequently and are a major issue in this universe. The thing is, why can't a belligerent stuff a willing militant in a warp-capable ship, have them fly directly into the enemy planet's atmosphere, and intentionally set the drive to collapse the ship into a black hole and destroy whatever happens to be near the ship when the warp drive detonates?
By mass-energy conversion, a one hundred ton ship (including warp drive and kamikaze bombers) would detonate with an energy of around 2.148 trillion tons of TNT, which is 2.5 times more energy than was released at the last Yellowstone eruption and almost 4,000 times more energy than has been released by all nuclear warfare and testing on Earth combined.
Obviously, the power of this weapon is so immense that if a few of them (<10) were used properly, an entire planet's population could be wiped out in a single attack. The other issue is, you can't see these weapons coming because they're arriving via warp drive: if the bomb has no geonic communicators on it, then the light containing information about the bomb's deployment will only reach ground zero after the bomb has already detonated, at which point there will probably be more obvious evidence.
This is a major issue for any kind of storytelling in this universe if there's a war going on. Pretty much everyone has access to warp bombs, which functionally act as perfectly-invisible planet-destroying weapons that are virtually impossible to stop. So why aren't these warp bombs ever used in actual warfare?