Unfortunately, there are a lot of things that nuke holders are taking advantage. Some of the causes:

1) Within about 10-20 second interval, everyone is getting the same list of 2-5 nuke targets,

2) People with multiple accounts. It's very easy to speedrun the game and get to the point where you can build nukes. The FOB event makes it easy to farm resources, and there are still some resource-farming exploits out there. Someone can easily farm enough resources and rotate between accounts so that every few hours or so, one of the accounts will generate a nuke (account A will generate a nuke at 12am everyday, account B at 3am, etc.). This will happen at a faster rate with higher staff levels (shaving off a few hours of development time) and if the person is willing to create more accounts and forgo sleep more regularly.

3) Blockade manipulation between people who have nukes. Basically, they're killing each others' staff and making sure they get detected and seen by each other so that they continue showing up in each others' retaliation list. This pretty much ensures that they have first dibs at each others' base, superseding the nuke targets tab.

4) Poor FOB players being encouraged to go after nukes, causing a blockade, and failing.

5) Phantom nukes. Even though someone may have just dismantled a nuke, they might be invaded at the same time.

6) Nuke-based trophies. Some people are rebuilding nukes because the nuke they built and wanted to disarm for the second nuke-based trophy just got stolen.

7) It's fairly easy for a defender to fulton his nukes before the invader gets to the final platform. The defender can take advantage of those 5 second or so of invincibility by falling fairly close to their nukes and not worry about dying.