You are postulating a weapon that is very powerful, has unique capabilities and must be commonly available. Yet it is no-where in any Traveller book.
This is supporting canon?
I prefer to believe that anti-ship weapons and SDBs (which we have ample support for in canon) were considered the preferred defence as no point defence was very effective. Especially against a Big Rock.
As to why we don't see more kinetic bombardment weapons, you aren't allways supporting attacks on a 1 G planet. A gravity powered weapon is little good against a low G world, a moon or a planatoid. We don't see much equivalent to Naval Gunfire Support with any weapon, so low orbit must be a dangerous place. Dumb rocks are not very accurate and need to be dropped from a even more vulnerable very low orbit. A "smart rock" is a missile and follows missile rules (with a bigger bang, maybe).
This is supporting canon?
I prefer to believe that anti-ship weapons and SDBs (which we have ample support for in canon) were considered the preferred defence as no point defence was very effective. Especially against a Big Rock.
As to why we don't see more kinetic bombardment weapons, you aren't allways supporting attacks on a 1 G planet. A gravity powered weapon is little good against a low G world, a moon or a planatoid. We don't see much equivalent to Naval Gunfire Support with any weapon, so low orbit must be a dangerous place. Dumb rocks are not very accurate and need to be dropped from a even more vulnerable very low orbit. A "smart rock" is a missile and follows missile rules (with a bigger bang, maybe).