A small group trying this plan, while making the secretive issues easier and increasing the likelihood of functional cooperatikn between the parties, magnifies the logistics issues to ludicrous levels, and would make it impossible for them to completely saturate all world governments to ensure they don't suffer nuclear retaliation.

Moreover, if the time between them getting their AGI and enacting their plan is inferior to the time it would take, say, the American military to crack ASI then AGI, then they'd be staring down the sights of an equally deadly beast to theirs with far more resources with which to counteract their own plans.

If they were to try and speed run a bio weapon, for example, and the Government managed to hole up in the Pentagon and finish this counter-AGI, a cure could be created for their bioweapon and the culprits subsequently nuked from existence.