Could you?
Arachnos employs psychic clairvoyants and precogs /en masse/. And has plenty of energy platforms and SPBs who can just null a long range nuke long before it reaches him.
You could /try/ to nuke the Rogue isles. You would probably fail. And Recluse would know you did it.
How may people does he have on his payroll who are /personally/ equivalent to a nuke and a whole lot less easy to counter? Apparently a bunch. They're aimed at Paragon city most of the time, but you know. Paragon has enough problems that it's counter invasion is basically. Longbow.
He can afford to turn attention to you for a while.
Mass carpet bombing?
Weeell.
Recluse has an army. An actual army. He has troops, air superiority in the isles and backs it up with super powered support and SPB level tech.
And telepaths. And seers. And massive numbers of killer robots. Arachnos drone firepower appears short ranged against hero/villian units, but against conventional forces, they probably have to the horizon laser capability. Just by virtue of actually being laser platforms.
So while all of the above applies, so does -
Send your conventional airforce to bomb the rogue isle and get shredded, because honestly Recluse appears to have the most modern military in the world that isn't Paragon city.
Send your ground forces and get mulched because a /whole lot/ of his Spider troops are wearing power armor and toting plasma cannons.
And their Seers have told them exactly where to setup to gun you down with /no possibility/ of any return fire.
Not to mention the host of killer robots designed to take down SPBs, no matter how much the struggle at the job. Or the Teleporting villains who will slaughter your command structure essentially at will if you make the commitment to try.
Or the various native power groups, which make the rogue isles a fundamentally hostile population /with superpowers/, as noted above.
/Vanguard/ might be able to invade the rogue isles. Malta if it had the troops (It's a 'secreet' conspiracy, it doesn't.).
Conventional Modern day militaries?
Are dogfood within days of engaging. /days/.
If the villians are feeling particularly motivated, possibly /hours/.
And this is not a comprehensive list of bad things. I didn't mention the traitorous conspiracy to turn the invading troops against each other (Hello, telepathy), the lethal bio plagues, the..well. We could go on.
Add this to the dead certainty that world militaries are going to be literally a century recovering from the rikti war, and no, USgov is not in a position to do anything about the rogue isles now.
And by the time they might concider it - either Paragon will have done so.
Or it will be so much worse.