Oh, and you know this how? The Thalmor's first objective is to remove Talos from the mythic. A free, independent Skyrim where they cannot enforce a Talos ban and around which humanity can rally a defense is a serious problem for them. They've got the empire by the gonads, so any threat from them is well under control. At the very least, if Cyrodiil makes any serious moves towards war, they'll know about it.
The answer is rather simple. Logistics. You can't capture a region the size of Skyrim without a very solid supply line and a good way of getting troops in place. The Thalmor have nowhere to land their troops in any proximity to Skyrim and supplies would have to be sailed in. That's no way to try and conduct a war. And no, the Thalmor don't have the Empire by the balls. It's a cold war with both sides trying to fool the other into making a critical mistake. The Empire currently can't mount an actual offensive against the Thalmor, but the Imperial Legion will still destroy any invasion force the Thalmor might send.
What also might happen if the Thalmor actually did land a serious force in Skyrim is that the Legion would march out and fall into the back of the Thalmor force. The Thalmor might learn about this but the Legion is a standing army and moving units of the Legion north isn't something that takes months to arrange. If it's done after the Thalmor invasion force has landed in Skyrim then there's not a whole lot the Thalmor can do about it.
Finally, I fully realise what the THalmor objective is, but I also realise that they're a patient bunch. They will of course attack Skyrim eventually, just not any time soon. They need to stop Talos worship but they need not do it in this particular century. Taking Cyrodiil and Hammerfell first would give the Thalmor a much, much better strategic and tactical situation, whereas a sea-based invasion of Skyrim is by and large doomed to fail miserably.
Skyrim is throwing what nations under the bus? High Rock and Cyrodiil are the only provinces left.
Essentially the entire mainland of Tamriel. With the Empire gone, all that remains are small nations that can't individually hope to stand against the Thalmor for long. You can try to forge alliances but alliances have fractures and if anyone would know how to take advantage of these, it's probably going to be the Thalmor.
We all know the story about why the empire "had" to give in to the Thalmor. Not all accept the defense. The random redguard farmer who gave me the Stormcloak quest in my current game said "the empire is in shambles, look at all we fought for and they surrendered anyway." So there you go. Obviously opinion is divided.
He's a Redguard. Of course he's going to be bitter and trashtalk the Empire. If you stand and watch as your girlfriend gets [censored] then she's going to get pissed at you, even if you have a broken arm and her rapist is the big, mean-looking thug who broke your arm. Rational arguments are irrelevant, because you stood and watched as she got [censored]!! Same thing with Redguards relative to the Empire.
That doesn't change the fact that the Empire needed a peace to survive or that the survival of the Empire is what keeps the Thalmor from engaging in open warfare just yet. It also doesn't change the fact that there was very little the Empire could've done to defeat the Thalmor back around 4E175. Sure, they could've helped kick the Thalmor out of Hammerfell, but then what could be done to protect the borders from constant raids that would no doubt be the Thalmor retribution?