Except that people hated gravity drills because they were annoying. This would be the same thing. It's not fun, or !fun!. It's an annoyance that just slows the game down.
I would like to add that in addition the gravity effect may be abused. For example, remember whippping boys or chokepoint planets? If there was a gravity effect, I can imagine people nuking one of those planets to make AI ships go the pace of a snail, then building the normal defenses as the neighboring planets can still provide supply.
Since in AIWC nukes cut supply, it is toatlly reasonable to make them prohibit anything to be built in AIW2. Of course, I know this idea is really crude. Yes, people may hate planetary gravity effect, but maybe that is just one nasty effect for both sides when you
really have to use a nuke.
They aren't supposed to be used after all. I am just proposing it to be actually
useful in an "detonate this or definitely lose" situation.
Update:
Although thinking twice, if you are doing a Fallen Spire campaign and nuke a planet in path of Exo... Hmm, that would slow things enough for you to warhead anything in that planet. I don't know, maybe make nukes +300AIP or so, and/or maybe let the AI charge up a brutal Exo wave after using it(which may motivate you to use
another one), would give it an absolutely "one time use" price tag, even on FS campaigns(although I regularly run on 700+ AIP on these games).
Frankly I think Nomad Beacon is more useful on killing what you
really don't want to show up on defense. It is one time: there is only one beacon. It costs a lot: a beacon hack, 30AIP for capturing Nomad 1, enormous metal and 500k energy for reparing the beacon, defending Exo waves sent out each minute when Beacon is activated, but... that thing destroys even the AI Homeworld, along with anything that are immune to nukes and warheads, and removes the entire planet from the map.
That is what I imagine a "nuke" should do. And looking at current nukes... It cost less resource, of course, but a lot more AIP, while doing much less. If the AI goes crazy after the humans detonate a nuke, why does it cost no more than structural AIP when a Nomad crashes on its homeworld? Then while a MkII nuke costs +500AIP for destroying all adjacent planets, what about a Nomad cutting off an entire section of a galaxy? If a MkIII nuke consumes the entire galaxy for +5000AIP, what about that Nomad trying to cut off the Human Home planet and AI Home planet?(I didn't try this, but according to the description, it should accomplish something similar.)